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The Journal of

Volume 39 Number 4 December 2005

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COVER: Cuban Black-Hawk {Buteogallus anthracinus gundlachii). Painting by Nils Navarro.

Contents

Taxonomic Status and Biology of the Cuban Black-Hawk, Buteogallus

ANTHRACINUS GUNDLACHII (AVES: AcCIPITRIDAE) . James W. Wiley and Orlando H. Garrido 351 I

Home Range and Habitat Use of Northern Spotted Owls on the Olympic

Peninsula, Washington. Eric D. Forsman, TimmothyJ. Kaminski, Jeffery C. Lewis,

Kevin J. Maurice, Stan G. Sovem, Cheron Ferland, and Elizabeth M. Glenn 365

First-cycle Molts in North American Falconieormes. Peter Pyie 378

Morphometric Analysis of Large Falco Species and Their Hybrids with

Implications for Conservation. Chris p. Eastham and Mike k Nichoiis 386

A Change in Foraging Success and Cooperative Hunting by a Breeding Pair

of Peregrine Falcons and Their Fledglings. Dick Dekker and Robert Taylor 394

Nesting Ecology and Behavior of Broad-winged Hawks in Moist Karst

Forests of Puerto Rico. Derek W. Hengstenberg and Francisco J.VUella 404

Raptor Abundance and Distribution in the Llanos Wetlands of Venezuela.

Wendy J. Jensen, Mark S. Gregory, Guy A. Baldassarre, Francisco J. Vilella, and Keith L. Bildstein .... 417

A Comparison of Breeding Season Food Habits of Burrowing Owls Nesting
IN Agricultural and Nonagricultural Habitat in Idaho. Coiieen e. Moulton,

Ryan S. Brady, and James R. Belthoff 429

Red-tailed Hawk Dietary Overlap with Northern Goshawks on the Kaibab

Plateau, Arizona. Angela E. Gatto, Teryl G. Grubb, and Carol L. Chambers 439

Bat Predation by Long-eared Owls in Mediterranean and Temperate Regions

OF Southern Europe. Ana Maria Garcia, Francisco Cervera, and Alejandro Rodriguez 445

Short Communications

Differential Effectiveness of Playbacks for Little Owls (Athene noctua) Surveys Before and
After Sunset. Joan Navarro, Eduardo Mmguez, David Garcia, Carlos Villacorta, Francisco
Botella, Jose Antonio Sanchez-Zapata, Martina Carrete, and Andres Gimenez 454

King Vultures (Sarcoramphus papa) Forage in Moriche and Cucurit Palm Stands. Marsha A. Schlee 458

Family Break Up, Departure, and Autumn Migration in Europe of a Family of Greater Spotted
Eagles (Aquila clanga) as Reported by Satellite Telemetry. Bernd-U. Meyburg, Christiane
Meyburg, Tadeusz Mizera, Grzegorz Maciorowski, and Jan Kowalski 462

Seasonal Patterns of Common Buzzard (Buteo buteo) Relative Abundance and Behavior in ^

POLLINO National Park, Italy. Massimo Pandolfi, Alessandro Tanfema, and Giorgia Gaibani ...... 466

New Nesting Record and Observations of Breeding Peregrine Falcons in Baja C al ifornia Sur,

Mexico. Aradit Castellanos, Cerafina Arglielles, Federico Salinas-Zavala, and Alfredo Ortega-Rubio 472

Letters

A Previously Undescribed Vocalization of the Northern Pygmy-Owl. Graham G. Frye 476

Book Review. Edited byjoelle Gehring 478

Information for Contributors 480

Index to Volume 39 484

The Raptor Research Foundation, Inc. gratefully acknowledges funds and logistical support
provided by Arkansas State University to assist in the publication of the journal.

THE JOURNAL OF RAPTOR RESEARCH

A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.

VoL. 39 December 2005 No. 4

J. Raptor Res. 39(4) :351— 364
© 2005 The Raptor Research Foundation, Inc.

TAXONOMIC STATUS AND BIOLOGY OF THE CUBAN BLACK-
HAWK, BUTEOGALLUS ANTHRACINUS GUNDLACHII

(AVES: ACCIPITRIDAE)

James W. Wiley^

USGS Maryland Cooperative Fish and Wildlife Research Unit, University of Maryland Eastern Shore,

1120 Trigg Hall, Princess Anne, MD 21853 US. A.

Orlando H. Garrido

1706 Calle 60 entre 17 y 19, Marianao 13 (Play a), La Habana, Cuba

Abstract. — ^We reevaluate the taxonomic status of the Cuban population of the Common Black-Hawk
{Buteogallus anthracinus) based on our examination of additional specimens, nests, eggs, and voice data.
Buteogallus a. gundlachii is smaller than mainland populations of anthracinus and differs from mainland
birds in plumage coloration and pattern. The common (alarm) call of gundlachii is a series of three or
four notes, differing from that of mainland anthracinus, whose call consists of 9-24 notes. In the Isla de
Pinos, Cuba, we observed gundlachii ediiing two species of land crabs (71.4%), centipedes (7.1%), lizards
(10.7%), mammals (7.1%), and a bird (3.6%). We consider Buteogallus gundlachii Cabanis 1854 (1855),
the Cuban Black-Hawk, to be a full species, endemic to Cuba, Isla de Pinos, and many of the cays of
the Cuban Archipelago.

Key Words: Common Black-Hawk; Buteogallus anthracinus; Cuban Black-Hawk; Buteogallus gundlachii;

Buteogallus subtilis; ecology; taxonomy.

ESTADO TAXONOMICO Y BIOLOGIA DE BUTEOGALLUS ANTHRACINUS GUNDLACHII (AVES:
ACCIPITRIDAE)

Resumen. — En este estudio re-evaluamos el estatus taxonomico de la poblacion cubana de Buteogallus
anthracinus (subespecie gundlachii) con base en examenes de especimenes adicionales, nidos, huevos y
datos de la voz. Los individuos de B. a. gundlachii son mas pequehos que los individuos de las poblaciones
continentales de B. anthracinus, y difieren de las aves del continente en la coloracion y patron del
plumaje. El llamado comun de alarma de gundlachii es una serie de tres o cuatro notas, mientras que
el llamado de anthracinus en el continente consiste de entre 9 y 24 notas. En la Isla de Pinos, Cuba,
observamos a gundlachii alimentandose de dos especies de cangrejos terrestres (71.4%), ciempies
(7.1%), lagartijas (10.7%), mamiferos (7.1%) y un ave (3.6%). Consideramos Buteogallus gundlachii
Cabanis, 1854 (1855) debe ser tratado como una especie distinta, endemica de Cuba, la Isla de Pinos
y muchos de los cayos del archipielago cubano.

[Traduccion del autores]

The New World genus Buteogallus Lesson, 1830
includes five species, mostly restricted to tropical
areas, including Great Black-Hawk {Buteogallus uru-

^ Email address: jwwiley@mail.umes.edu

bitinga) of the lowlands of Mexico to northern Ar-
gentina, Savanna Hawk {B. meriodionalis) inhabit-
ing savannas and marshes of western Panama to
northern Argentina, Rufous Crab-Hawk (B. aequi-
noctialis) occurring in mangroves of northeastern

351

352

Wiley AND Garrido

VoL. 39, No. 4

Venezuela to eastern Brazil (Parana), and Man-
grove Black-Hawk {B. subtilis), which is restricted
to the Pacific coasts and rivers of El Salvador south
to northwestern Peru. The Common Black-Hawk
(Buteogallus anthracinus, Deppe 1830) ranges from
southwestern United States, south to extreme
northern South America (coastal Venezuela to
northeastern Guiana) , Colombia, to northern
Peru, including Trinidad, and some of the West
Indies (Bond 1950, American Ornithologists’
Union 1998). One of the West Indian populations
{B. a. cancrivorus Clark 1905b) is restricted to St.
Vincent, St. Lucia, Union Island (Grenadines), and
Grenada (accidental and doubtful in last two is-
lands; no specimens taken; Clark 1905a, 1905b,
1905c, Bond 1950, Evans 1990) in the Lesser An-
tilles, whereas the only other Antillean population
{B. a. gundlachii Cabanis 1854 [1855]) occurs in
Cuba and its satellites. The taxonomic status of the
Cuban population has been controversial, with
some considering the form as a full species, Buteo-
gallus gundlachii (as originally described by Cabanis
[1854, actually 1855]) instead of Buteogallus anth-
racinus gundlachii (American Ornithologists’ Union
1998) . Among those authorities who have consid-
ered the Cuban form gundlachii conspecific with
the continental species {anthracinus) are Sharpe
(1874, 1899), Cory (1887, 1892), Bangs and Zap-
pey (1905), Bond (1956a, 1956b), Amadon (1961),
Brown and Amadon (1968), Mayr and Short
(1970), Stresemann and Amadon in Mayr and Cot-
trell (1979), Palmer (1988), Sibley and Monroe
(1990), Ferguson-Lees and Christie (2001), Dick-
inson (2003), and others. Conversely, other au-
thors have considered gundlachii different from Bu-
teogallus anthracinus at the species level: Cabanis
(1855), Gundlach (1854, 1865-1 866a, 1865-1 866b,
1871, 1876), Ridgway (1876), Gurney (1876, 1934),
Bangs (1905), Swann (1921-1922, 1930), Peters
(1931), Bond (1936), Hellmayr and Conover
(1949), Friedmann (1950), Monroe (1963, 1968),
Wetmore (1965), and others. Some of these au-
thors subsequently changed their opinions on the
Cuban form’s status, later considering gundlachii
conspecific with anthracinus (e.g., Gundlach 1893,
Bond 1950, 1956a, 1956b). With rare exception,
however, previous evaluations did not consider the
important characteristics of breeding biology and
voice, mainly because of the limited knowledge of
the Cuban form resulting from the difficulty in
reaching its breeding habitats. The lack of natural
history information is not unique to gundlachii, but

is also true for other forms of the genus Buteogallus,
e.g., anthracinus and subtilis, which are currently
recognized as different species (Aldrich and Bole
1937, Amadon 1982, Mayr and Cottrell 1979, Stiles
and Skutch 1989, Sibley and Monroe 1990, Amer-
ican Ornithologists’ Union 1998, Ridgely and
Greenfield 2001), but with reservation by some au-
thors (Stiles and Skutch 1989, American Ornithol-
ogists’ Union 1998, Ridgely and Greenfield 2001).

Here, we reevaluate the taxonomic status of the
Cuban population of Buteogallus anthracinus gund-
lachii, based on our examination of more speci-
mens, nests, eggs, and behavioral data, especially
vocalizations, than were considered by previous
workers. All published work on the Cuban form
has been based on information from the few spec-
imens collected before 1960, all of which are de-
posited in foreign institutions. In this study, we in-
clude specimens in North American and Cuban
collections, including those collected after 1960,
and not evaluated previously.

Our main comparison in this assessment is with
anthracinus, the taxon most often linked to gund-
lachii. In these comparisons, we refer to Cuban
populations as gundlachii and other forms as anth-
racinus. It is not the purpose of this contribution
to speculate on the taxonomic status of Buteogallus
subtilis (including the three subspecies), although
we make some comparisons between subtilis and
gundlachii.

Study Area

Many of the observations reported here were made
during our 30 yr of field experience throughout Cuba.
We made more intensive observations of nesting black-
hawks from 1996 to 1998 at the Los Indios Ecological
Reserve, Isla de Pinos (now Isla de la Juventud). M^or
vegetational communities at Los Indios include: (1) man-
grove forest formation, characterized by black mangrove
(Avicennia germinans) and red mangrove {Rhizophora man-
gle); (2) semi-deciduous gallery forests, with prominent
Cuban royal palm (Roystonea regia), beach hibiscus {Ht-
hiscus tiliaceus), and pond apple {Annona glabra); (3) the
open forest (savanna) formation of an open pine {Pinus
caribaea and P. tropicalis) and Cuban bottle palm ( Colpoth-
rinax rmightii) , with silver saw palm (Acoelorraphe wrightn)
and a sparse undergrowth; and (4) the pine-barren for-
mation, with pines and palms, and an undergrowth pre-
dominantly of Pachyanthus cubensis, P. poiretii, Kalmiella ag-
gregata, Miconia delicatula, Polygala uncinata, Lyonia
myrtilloides, and Pinguicula filifolia (Jennings 1917, Alain
1946). Black-hawk observations were made mainly in the
mangrove and gallery forests. Additional intensive obser-
vations in red and black mangrove habitats were made
in Cienaga de Zapata in December 1999. An elevated
road bed, lined with Casuarina equisetifolia and scrub veg-

December 2005

Cuban Black-Hawk Status and Biology

353

elation, bisects the mangrove forest where we made our
observations near Playa Larga.

Methods

We examined specimens of Buteogallus a. anthracinus
(N = 37), B. a. gundlachii (12), B. a. cancrivorus (4), B.
subtilis (25), B. aequinoctialis (3), and B. urubitinga (24)
deposited in the Field Museum of Natural History (Chi-
cago), Museum of Comparative Zoology (Harvard Uni-
versity), American Museum of Natural History, United
States National Museum of Natural History, Academy of
Natural Sciences of Philadelphia, Louisiana State Univer-
sity Museum of Natural History, Museo Nacional de His-
toria Natural de Cuba (La Habana), and Instituto de Eco-
logia y Sistematica (Cuba) (Table 1). Conventional
measurements of wing chord (flattened against the rul-
er), tail, tarsus, and exposed culmen were taken to the
nearest 0.1 mm with calipers. Egg masses were measured
to the nearest gram using spring scales. We present sum-
mary descriptive statistics (mean, SD, and range) for the
specimens. We plotted body measurements to assess the
pattern of spatial segregation among populations and
forms. The hypothesis of separation derived from the
plots of body measurements was tested using discriminate
function analysis (DFA; Kleinbaum and Kupper 1978).
SPSS (1999) for Windows was used to run DFA.

Results

Morphometries and Plumage. Adult morphology.
Our examinations of the two taxa of B. anthracinus
(anthracinus and gundlachii) revealed differences in
size and coloration. We found sexual size dimor-
phism in three of the measurements taken of spec-
imens of mainland anthracinus (Table 1). There-
fore, size comparisons between anthracinus and
gundlachii were made within sex; i.e., male anthra-
cinus with male gundlachii and female anthracinus
with female gundlachii. Tarsal length was not dif-
ferent in either population, so for comparing anth-
racinus with gundlachii tarsi we combined male and
female measurements for that morphometric pa-
rameter. Only measurements of wing and exposed
culmen for gundlachii revealed sexual size dimor-
phism (P < 0.01; Table 1), although the small sam-
ple size of females (N — 5) precluded a reliable
analysis. Measurements of gundlachii yielded a
mean Dimorphic Index (Storer 1966) of 6.9, com-
pared with a mean index of 5.6 for anthracinus (Ta-
ble 1).

Birds from Cuba (gundlachii) are substantially
smaller than mainland (anthracinus) birds in some
conventional measurements, including wing chord
in both sexes and tail length in males (Table 2).
Also, tarsal lengths (combined male and female
measurements) were significantly different be-
tween the two forms (P — 0.001). A stepwise selec-

tion procedure within DFA revealed wing chord,
tail length, and exposed culmen were the most im-
portant of the size variables measured. Plots con-
trasting these variables within sex showed anthra-
cinus and gundlachii tended to occupy generally
distinct regions of the morphological space (Fig.
1 ).

To further examine size differences between the
two populations, we used linear discriminant anal-
ysis to classify specimens into two groups (“race”),
mainland anthracinus and Cuban gundlachii, using
lengths of wing chord, tail, culmen, and tarsus as
predictors. For male anthracinus, the analysis pro-
duced a true group classification proportion of
0.938 (15 of 16 correctly classified) and 0.857 (6
of 7 correctly classified) for gundlachii males, for
an overall proportion correct of 0.913 (21 of 23)
(Wilks’s lambda = 0.375; = 17.646; df = 4, P<

0.001). For females, the analysis produced a true
group classification proportion of 0.857 (18 of 21)
for anthracinus and 0.800 (4 of 5) for gundlachii
individuals, for an overall proportion correct of
0.846 (22 of 26) (Wilks’s lambda = 0.4.95; =

14.781.1; df = 4, P< 0.005).

The four adult female St. Vincent (B. a. canen-
vorus) specimens we examined were somewhat
larger in wing chord (x = 389 ± 7.63, range =
385-401; t = -4.99, P = 0.002, df = 6) than gund-
lachii females, whereas we found no difference be-
tween the two island forms in tail (213.3 ± 12.4;
range = 200-230; t - -1.83, P > 0.05, df = 6),
culmen (27.3 ± 0.8; range = 26.8-28.4; t = 0.60,
P > 0.05, df = 5), or tarsus (85.5 ± 6.4; range =
81.0-94.9; t = -1.63, P> 0.05, df = 4) length. We
found no differences (P > 0.05) in measurements
between anthracinus and cancrivorus.

In general coloration, gundlachii differs from B.
anthracinus and B. subtilis in being chocolate-
brown, not slate blackish or even black as in the
latter two forms. However, some specimens of anth-
racinus, especially of the race cancrivorus, have a
tendency to be less blackish, almost dark brown.

The underparts feathers of gundlachii have a
light (brownish-gray) edge, more conspicuous to-
ward the abdominal region and more broadly
edged on the alula coverts than in anthracinus, with
the edging on the terminal alula coverts becoming
white bands. The margins of the flank and thigh
feathers are heavily marked, forming a series of
bands, although these bands tend to disappear in
older birds. The shoulder feathers are boldly
barred in white, contrasting with the chocolate-

354

Wiley AND Garrido

VoL. 39, No. 4

Table 1. Sexual size dimorphism in four body measurements from specimens of Buteogallus anthracinus (mainland
Buteogallus a. anthracinus -aind Cuban B. a. gundlachii) , B. subtilis, B. aequinoctialis, and B. urubitinga, expressed as mean,
standard deviation, range, and sample size (in parentheses). Statistical analyses are between-sex comparisons (two-
sample t-test; equal variances not assumed) .

Species

Structure

Sex

Male

Female

Signif-

icance®

D.l.^

Buteogallus anthracinus

Wing

371.69 ± 11.95 (16)

385.19 ± 11.21 (21)

-3.50

0.001

3.6

341-393

360-421

Tail

195.50 ± 7.40 (16)

213.81 ± 10.61 (21)

-6.18

0.0001

8.9

183-210

190-230

Exposed culmen

26.27 ± 0.82 (16)

27.40 ± 1.25 (20)

3.24

0.003

4.2

25.1-28.1

23.6-30.3

Tarsus

85.94 ± 2.65 (16)

85.42 ± 4.00 (21)

0.48

0.636

-0.6

80-90.0

80.3-92.7

Mean D.I.

4.0

Buteogallus gundlachii

Wing

342.71 ± 12.16 (7)

363.00 ± 8.43 (5)

-3.41

0.008

5.8

323-370

350-372

Tail

179.29 ± 9.12 (7)

191.60 ± 22.16 (5)

-1.15

0.313

6.6

167-197

182-233

Exposed culmen

25.32 ± 0.69 (7)

27.54 ± 0.61 (5)

-5.84

0.0001

8.3

24.5-28.5

26.7-28.1

Tarsus

81.33 ± 3.57 (6)

79.67 ± 3.56 (5)

0.77

0.464

-2.1

75.4-87

79.0-87.7

Mean D.I.

4.7

Buteogallus subtilis

Wing

348.0 ± 13.68 (12)

352.31 ± 13.43 (13)

-0.79

0.436

1.2

330-370

328-373

Tail

189.92 ± 14.58 (12)

191.69 ± 8.65 (13)

-0.37

0.719

0.9

168-220

180-205

Exposed culmen

25.46 ± 2.06 (12)

26.56 ± 1.56 (12)

-1.47

0.157

4.2

19.7-27.8

23.1-28.8

Tarsus

79.78 ± 3.09 (11)

79.55 ± 2.76 (13)

0.19

0.848

-0.3

73.3-84.1

75.0-84.0

Mean D.I.

1.5

Buteogallus aequinoctialis

Wing

315.5 ± 0.71 (2)

322 (1)

315-316

Tail

155.0 ± 2.83 (2)

155 (1)

153-157

Exposed culmen

23.55 ± 0.92 (2)

16.8 (1)

22.9-24.2

Tarsus

74.5 ± 3.54 (2)

72.8 (1)

72-77

Buteogallus urubitinga

Wing

384.94 ± 16.68 (16)

389.63 ± 18.36 (8)

-0.61

0.555

0.1

362-412

365-415

Tail

225.13 ± 13.50 (16)

234.63 ± 17.54 (8)

-1.35

0.206

4.1

190-250

210-260

Exposed culmen

29.72 ± 1.05 (16)

30.78 ± 2.20 (8)

-1.84

0.103

3.5

26.7-30.9

27.2-34.2

Tarsus

112 ± 8.25 (16)

113.16 ± 7.76 (8)

-0.11

0.910

1.0

85.9-118.9

98.8-123.0

Mean D.I.

2.2

® Significance, * = P < 0.05, ns = not significant.
D.I. = Dimorphic Index (Storer 1966).

December 2005

Cuban Black-Hawk Status and Biology

355

Table 2. Mean, standard deviation, and sample size (parentheses) for wing chord, tail, culmen, and tarsus length
for mainland {Buteogallus a. anthracinus) and Cuban {Buteogallus a. gundlachii) populations of the Common Black-
Hawk. Statistical analyses are within-sex comparisons (two-sample <-test; equal variances not assumed) between main-
land and Cuban specimens, except for tarsus, for which we found no sexual size dimorphism.

Structure

Sex

Taxon

B. A. ANTHRACINUS B. A. GUNDLACHII

Signieicance^*

Wing

371.69 ± 11.95 (16)

342.71 ± 12.16 (7)

5.28

<0.001

385.19 ± 11.21 (21)

363.00 ± 8.43 (5)

4.94

0.002

Tail

195.50 ± 7.40 (16)

179.29 ± 9.12 (7)

4.14

0.003

:)4

213.81 ± 10.61 (21)

191.60 ± 22.16 (5)

2.14

0.099

Exposed

26.27 ± 0.82 (16)

25.32 ± 0.69 (7)

2.86

0.013

culmen

27.40 ± 1.25 (20)

27.54 ± 0.61 (5)

-0.36

0.728

Tarsus

M and F’’

85.64 ± 3.45 (37)

80.57 ± 3.49 (11)

4.24

0.001

® Significance, * = P < 0.05, ns = not significant.

^ Male and female tarsus data combined because specimens did not display sexual size dimorphism.

brown ground color. Remiges are dark brown, with
wing coverts edged in grayish-cinnamon, especially
the secondaries. The undersides of primaries and
some secondaries have an extensive white patch,
which constitutes the most distinctive character of
the Cuban form. In subtilis, and especially anthra-
cinus, this patch is mottled with grayish-brown. The
tertiaries of gundlachii are heavily mottled grayish.
This mottling is similar to the coloration of the
primaries and secondaries of anthracinus, which
has only an inconspicuous whitish patch on the un-
dersides of these feathers. On the other hand,
some specimens of subtilis display more white in
this region than does anthracinus, but do not ap-
proach the amount shown in gundlachii.

The upperparts in gundlachii are also brown,
with brownish-gray or with a trace of cinnamon on
the feather margins. The head and pileum are uni-
formly chocolate brown. The rectrices are darker
brown, almost blackish, with a broad white band
of variable width (averaging 40 mm) in the middle
of the tail. The tip of the tail is edged in white (as
wide as 13 mm), which is a purer white than in
anthracinus and subtilis. The feet and cere are yel-
low, the claws are black, and the iris is dark brown.
The bill is blackish at the tip, becoming more yel-
lowish toward the base on maxilla and mandible.

Immature morphology. Immature gundlachii individ-
uals are not chocolate brown ventrally, but rather
whitish, and heavily mottled with brown, having
some feathers with considerable beige suffusion.
Many feathers are mottled with medallion-like
marks, whereas others are marked with elongated
blotches, and some with streak-like dashes; these

marks are seldom present in fully-feathered im-
mature birds. The sides of the face and throat are
whitish, speckled with hrown. The pileum, nape,
and neck are heavily mottled or spotted with
brown on a light (white or beige) background.
Flanks and thighs also display considerable varia-
tion, with younger birds showing a lighter (whitish
to brownish-beige) background, whereas older
birds display more mottling or barring. The thighs
are distinctly barred with light and dark bands in
subtilis and anthracinus, whereas gundlachii has mot-
tled or very lightly barred thighs.

The white patch of the underside of primaries is
even more expanded and conspicuous in subadult
than in adult gundlachii. Also, the subadult’s tail is
distinct from that of the adult’s tail. When still not
in full adult plumage, the subadult’s tail shows
remnants of several (as many as nine) thin, brown-
ish bands, instead of displaying a single broad
white band in the middle of the tail as in the adult.
Some bands are complete, whereas others are
somewhat broken. In Cuban birds, these bands are
straight and parallel, whereas in the other forms
they are oblique (chevron-like), as well as being
much wider than in gundlachii. The bands become
less delimited toward the tip; compared with the
adult, the white tip of the subadult’s tail is less de-
marcated, more grayish than white, and becomes
browner from the tip toward the base.

Natural History. Habitat. Although we occasion-
ally observed black-hawks within the white sand
palm savanna of Los Indios, Isla de Pinos, nearly
all observations were made in the coastal zone, pri-
marily in mangrove forests or at the edges of that

356

Wiley AND Garrido

VoL. 39, No. 4

Male

Female

420
410
400
O) 390
5 380

370
360
350

23.5 24.5 25.5 26.5 27.5 28.5 29.5 30.5 23.5 24.5 25.5 26.5 27.5 28.5 29.5 30.5

Culmen Culmen

230
220
210

_ 200
<0

^ 190

180
170
160

75 80 85 90

Tarsus

Figure 1. Plots contrasting body measurements of specimens of mainland Buteogallus anthracinus anthradnus (solid
dots; = 16 males, 21 females) and Cuban B. a. gundlachii (open circles; N = 7 males, 5 females).

habitat. Hawks hunted in the sparsely-vegetated
mangrove pannes and flooded openings, where
they foraged by perching in young or dead man-
groves. We also saw black-hawks foraging or roost-
ing in beach and coastal habitats, frequently perch-
ing in windbreaks of Casuarina equisetifolia at the
edge of mangroves and dirt roads.

Nidification. We examined eight nests at Los In-
dios within the period of 14-27 May 1996-98. All

contained eggs, except the nest examined on 27
May 1996, which had one chick. During our obser-
vations at Isla de Pinos, which were well into the
breeding season, we observed no aerial courtship,
although individual gundlachii regularly soared si-
lendy for short periods above their nesting areas.

Of the eight gundlachii nests we examined at Los
Indies, half were placed in black-mangroves and
half in red-mangroves (Table 3) . Each of the nests

Table 3. Nest and contents data for eight Buteogallus anthracinus gundlachii nests at Los Indios, Pinos, Cuba, 1996-98.

December 2005

Cuban Black-Hawk Status and Biology

357

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was in the subcanopy, shaded by foliage and was
constructed completely of Avicennia and Rhizophora
twigs. The nests showed a large range of sizes,
probably the result of additions made in successive
years. Two of the nests we monitored from 1996
through 1998 were reused by black-hawks, and in-
creased in size with the addition of more nest ma-
terials in subsequent years. All nests examined at
Los Indios contained fresh or older lining materi-
als, consisting of green leaves and sprigs of Avicen-
nia and Rhizophora, and some debris. Both adults
were observed bringing green lining material to
nests.

Nests had notably deep bowls (Table 3) and
when adults were on nests incubating or brooding,
they remained low in the bowl and were difficult
to detect. During our inspections of nests at Los
Indios, adults at three nests regularly perched plac-
idly within 2 m of us while we measured eggs and
chicks. Adults at a fourth nest were somewhat more
aggressive, but the pair only flew low above our
heads, occasionally calling, and vocalized from a
nearby perch while we measured eggs.

We measured 11 eggs at Los Indios (Table 3).
Three eggs collected by O. H. Garrido in Cayo
Candles (Archipielago de los Canarreos; deposited
at Instituto de Ecologia y Sistematica) measured
55.16 X 44.1 mm, 55.8 X 42.6 mm, and 57.08 X
42.34 mm. The 14 gundlachii eggs we measured av-
eraged 55.87 ± 0.69 (range = 54.7-57.08) X 42.71
± 0.62 (range = 41.9—44.1) mm. Eggs of gundla-
chii are typically short sub-elliptical to elliptical,
with a finely granulated texture. Eggs have a dull
grayish-white ground color, sometimes with a
greenish or bluish cast early in incubation, and are
marked with spots and blotches of dark or reddish-
brown, particularly at the larger end. Clutch sizes
at Los Indios averaged 1.57 ± 0.53 {N — 8; range
= 1-2) eggs (Table 3). The egg of gundlachii is
usually more colored (bluish to greenish suffu-
sion) than those of anthracinus or subtilis, which are
typically grayish or whitish (Bent 1937, Wetmore
1965, O. Garrido pers. obs.).

Diet and foraging behavior. Cuban birds were
found to feed on a variety of prey (Table 4) . No-
table was the lack of fish prey, although fishes were
available in tidal channels in the study area. How-
ever, twice, hawks were observed wading in shallow
tidal channels and making foot thrusts at probable
fish prey. During our observation periods (May-
June) at Los Indios, land crab populations were
particularly high, and crabs were active and con-

358

Wiley AND Garrido

VoL. 39, No. 4

Table 4. Prey of Buteogallus anthracinus gundlachii at Los Indios, Isla de Pinos, Cuba, 1996—1998, and Cienaga de
Zapata, Cuba, 1999-2000.

Prey

Number (%)

Observed Brought
TO Nest

Prey Remains

Observed Captures

Total (%) All
Observations

Invertebrates

Crab

Cardisoma guanhumi

18 (64.3)

Ucides cordatus

2 (7.1)

Centipede sp.

2 (7.1)

Totals (invertebrates)

6 (21.4)

14 (50.0)

2 (7.1)

22 (78.6)

Vertebrates

Reptiles

Lizards

Anolis spp.

2 (7.1)

Ameiva auberi

1 (3.6)

Totals (reptiles)

2 (7.1)

1 (3.6)

3 (10.7)

Birds

Sora Porzana Carolina

1 (3.6)

Totals (birds)

1 (3.6)

Mammals

Rattus rattus

2 (7.1)

Totals (mammals)

2 (11)

2 (7.1)

Total (vertebrates)

2 (7.1)

4 (14.3)

6 (21.4)

Total (all observations)

8 (28.6)

18 (64.3)

2 (7.1)

spicuous in the early mornings and evenings, when
most of our observations of prey delivery and cap-
tures were made. In December 1999, we also ob-
served gundlachii capturing several crabs {Cardiso-
ma guanhumi) along the coast of Cienaga de
Zapata, where the hawks hunted from a mixed
mangrove- equisetifolia-codistal scrub zone.

During our observations in the Los Indios man-
grove habitat, gundlachii displayed passive still
hunting from low (x = 1.3 ± 0.94; range = 0.2-3
m; N = 54) mangrove tree perches or from the
ground. Prey captures were made in a low-angle
flight, snatching the item (all observations of
crabs) and continuing to a nearby perch, or the
hawk landed near the crab and stalked it on foot.
Once the hawk grasped the crab, it controlled the
claws and legs on either side of the prey with its
feet, then removed the carapace with a quick tug
at the head region using its bill.

We found apparent caches of uneaten, though
dismembered, land crabs near (range = 5-20 m)
used gundlachii nests. However, we did not observe

hawks returning to the caches to feed on the stock-
piled crabs.

Although B. a. anthracinus has been observed
(O. Garrido pers. obs.) in Mexico hunting at the
edge of a meadow in a fashion similar to that of
the coursing behavior of the Northern Harrier
{Circus cyaneus), gundlachii was not observed for-
aging aerially in an active manner.

Vocal behavior. The common call of gundlachii is
a series of three or, uncommonly, four notes, with
emphasis on the first two elements, suggesting its
Cuban common name, BA-TIS-ta (Gundlach 1893,
Garrido and Schwartz 1969, Garrido and Kirkcon-
nell 2000; Fig. 2A). The call has a much shorter
duration and fewer elements than in other popu-
lations of Buteogallus anthracinus (Table 5). The
common call of mainland anthracinus consists of 9-
24 notes, with the middle to the final third of the
notes accentuated (Fig. 2C-F, Table 5). Stiles and
Skutch (1989) characterized the call of mainland
anthracinus as ''klee klee klee KLEE KLEE klee kle kle
keki ki." The comparable call of cancrivorus con&i&Xs,

December 2005

Cuban Black-Hawk Status and Biology

359

Figure 2. Sonographs of common (alarm) calls of Buteogallus species. A. Buteogallus anthradnus gundlachii, showing
typical three element “ba-tis-ta” phrase, Cuba (G.B. Reynard), B, Buteogallus a. cancrivorus, St. Vincent (J. Roche,
courtesy British Library Sound Archive) . C, Buteogallus a. anthradnus, Costa Rica (Cornell Library of Natural Sounds
27216). D. Buteogallus a. anthradnus, Venezuela (R Schwartz). E. Buteogallus a. anthradnus, male, Arizona (courtesy J.
Schnell). F. Buteogallus a. anthradnus, female, Arizona (courtesy J. Schnell). G. Buteogallus urubitinga, Venezuela (P.
Schwartz) . H. Buteogallus aequinoctialis, Surinam (Paul Donahue, courtesy British Library Sound Archive) .

Table 5. Characteristics {x ± SD, range in parentheses) of the common (advertisement) call of Buteogallus anthraanus anthraanus, B. a. cancnvorus,
gundlachii, B. urubitinga, and B. aequinoctialis.

Wiley AND Garrido

VoL. 39, No. 4

360

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of a large number of elements (22-37), with em-
phasis on several middle elements (Fig. 2B, Table
5). Similarly, the common call of B. subtilis is sub-
stantially different from that of gundlachii, consist-
ing of several, rapidly repeated elements, described
by Ferguson-Lees and Christie (2001) as a series of
shrill whistles, indistinguishable from anthracinus.
The call of Buteogallus urubitinga consists of a single
note, drawn out in a high shrill keeeeeeeeh" (Fer-
guson-Lees and Christie 2001; Fig. 2G), whereas
that of Buteo aequinoctialis is a distinct series of whis-
tle-like notes (Ferguson-Lees and Christie 2001;
Fig. 2H, Table 5).

Discussion

As is normal among most birds of prey, female
gundlachii are somewhat larger than males, with
culmen and wing length significantly different be-
tween genders. Sexual size dimorphism was less ev-
ident in anthracinus {x Dimorphic Index = 4.0)
than gundlachii, where we found a mean Dimor-
phic Index of 4.7 with males significantly larger
than females in wing and culmen length (Table 1).
Snyder and Wiley (1976) reported a lower index
(2.7) of sexual size dimorphism for B. anthracinus.

Whereas measurements of selected body parts
did not show complete distinction between anth-
racinus and gundlachii (Table 2, Fig. 1), Cuban
birds were consistently smaller or at the small end
of the range for anthracinus measurements. In con-
trast to our measurements. Bangs (1905) partly
based his determination of separating gundlachii
from anthracinus on the former being slightly larg-
er than the latter, and in having a decidedly heavi-
er, broader bill. As a general pattern, Schnell
(1994) noted that Common Black-Hawks of conti-
nental (inland) North and Central America are
largest. Mainland anthracinus populations inhabit-
ing mangrove habitat tend to be smaller and
browner than others. The race B. subtilis rhizopho-
rae, which inhabits mangrove habitat (Monroe
1963, 1968, Blake 1977), shows a dark-brown plum-
age. Our observations revealed that Cuban birds,
also mangrove inhabitants, are consistently brown-
er with substantial differences in plumage pattern
compared with mainland birds. Thus, such color
differences may be a result of ecological parallel-
ism, rather than of phylogenetic relationships.

The species of Buteogallus are partial to wetlands,
swampy woods, and seacoasts (Amadou 1982). In
its mainland range, anthracinus has been charac-
terized as inhabiting woodlands around coastal

December 2005

Cuban Black-Hawk Status and Biology

361

swamps, ponds, and streams, and especially man-
groves in the swampy woodlands adjacent to the
poorly-drained inlands that are affected by tide-
waters (Phillips et al. 1964, Wetmore 1965, Davis
1972, Schnell 1994). Wetmore (1965) noted that
along large rivers they extend their range farther
inland. Thomas (1908) reported anthracinus in
stretches of sand dunes and savannas with clumps
of palmettos and pines. The Cuban population
shows a similar preference for lowland coastal ar-
eas. Gundlach (1893) and Bangs (1905) noted
gundlachii was found only in mangrove swamps and
on the banks of large rivers. In broad contrast, the
other West Indian population, Buteogallus anthraci-
nus cancrivorus of St. Vincent, mainly keeps to the
high wooded valleys, although it seldom occurs far
from water (Lister 1880, Clark 1905b, Bond
1956a).

Cuban populations of the black-hawk breed
from January through June (Garrido and Kirkcon-
nell 2000) , with egg-laying occurring in late March
or April. Bangs (1905) collected a female contain-
ing a soft-shelled egg and found another tending
a nest on 15 April. Bond (1950) reported a nest
with a newly-hatched chick on 4 April. Garrido and
Schwartz (1969) and Valdes Miro (1984) com-
mented gundlachii builds its nest at a considerable
distance above the ground. Gundlach (1876) re-
ported a nest at 8 “varas” (6.8 m), whereas Bond
(1936) noted one at 6.2 m.

Nests of the Cuban form are typically rough
structures of twigs, lined with green leaves and,
sometimes, debris (Gundlach 1893, Bond 1936,
Garrido and Schwartz 1969, Valdes Miro 1984).
Bond (1936), describing nests found in St. Vincent
{B. a. cancrivorus) and Cuba {gundlachii), noted,
“The nest, a rough mat of sticks, is placed at vari-
ous elevations in trees.” All nests located by us at
Los Indios in 1996-98 were in mangroves {Avicen-
nia, Rhizophora). In contrast, Bond (1936) de-
scribed black-hawk nests in St. Vincent as “placed
on top of clumps of mistletoe and were rather
small.” As Bond (1936) suggested, nests of the Cu-
ban species are somewhat larger than those of
birds in St. Vincent. Schnell (1994) gave the di-
mensions of mainland anthracinus nests as ranging
from 38 cm diameter X 20 cm deep to 1.2 m di-
ameter X 0.67-1.2 m deep. Bangs (1905) and
Bond (1936) also noted gundlachii re-used nests in
more than one season, which we believe accounts,
in part, for the larger nest size of Cuban birds.

Black-hawks at Los Indios were remarkably non-

aggressive toward humans at their nests and al-
lowed us to approach much closer than other local
raptor species tolerated, perhaps relying on their
cryptic behavior to avoid detection at the nest.
Others have also noted this tolerance in Cuban
black-hawks (Todd 1916, Barbour 1923, Garrido
and Schwartz 1969).

Schnell (1994) reviewed available egg specimens
for Buteogallus anthracinus, summarizing mean
measurements from Bent (1937) as 57.3 X 44.9
mm {N = 60 eggs) and examples in the Western
Foundation of Vertebrate Zoology as 57.30 X 45.50
mm (V = 12 clutches, 19 eggs; range = 52.61-
62.02 mm length, 42.69-47.35 mm breadth). Eggs
of anthracinus we measured at the Delaware Mu-
seum of Natural History averaged 57.46 (53.1-
63.2) X 45.25 (41.7-49.1) mm {N = 13 clutches,
21 eggs). Interestingly, an egg reported from St.
Vincent is at the high end for the species: 61 X 47
mm (Bond 1936) and exceeds the range for gund-
lachii. Eggs of gundlachii we measured at Los Indios
averaged only slightly smaller than those of main-
land B. anthracinus analyzed by Schnell (1994).
Gundlach (1876) reported that Cuban eggs mea-
sured 58 X 45 mm, whereas Bangs (1905) reported
56 X 45.5 mm. Measurements presented by Valdes
Miro (1984) are obviously in error; i.e., x = 56.0
(range = 55.0-57.0) X 24.6 (23.0-26.5) mm. The
mean mass (61.0 ± 1.8 g) of eggs we measured at
Los Indios was somewhat lighter compared with
SchnelFs estimated mean mass of 63.8 g for anth-
racinus.

Although we observed differences in egg color-
ation and pattern among anthracinus, subtilis, and
gundlachii, these characters show considerable var-
iation and do not appear to be a good character
for determining relationships (L. Kiff pers.
comm.).

Schnell (1994) noted that, in general, clutch size
of Buteogallus anthracinus decreased from two eggs
in the northern range to one in the southern
range; several reported three-egg clutches were
questionable. Clutch sizes at Los Indios fell within
that range, averaging 1.57 eggs per clutch.

Buteogallus anthracinus feeds mainly on inver-
tebrates and lower vertebrates, with occasional
small birds or mammals in the diet (Schnell 1994).
Eor mainland populations, Thomas (1908) report-
ed anthracinus preying on burrowing land crabs,
which form almost the sole diet of the hawks in
British Honduras (Belize). The St. Vincent popu-
lation {B. a. cancrivorus) reportedly feeds on cray-

362

Wiley AND Garrido

VoL. 39, No. 4

fish and freshwater crabs (Lister 1880). In Cuba,
Gundlach (1893) reported remains of crustaceans,
as well as frogs, snakes, and fishes in the stomachs
of black-hawks. Barbour (1943) reported land crabs
as its prey in Cuba. Garrido and Kirkconnell
(2000) reported its prey as mainly crabs and birds,
whereas Ramsden (C. Ramsden, Museo de His-
toria Natural, Universidad de Oriente, Santiago de
Cuba unpubl. data) noted the hawk fed on crabs
and fishes.

The hunting behavior of Buteogallus, in general,
has been characterized as sluggish. Schnell {in
Palmer 1988, 1994) noted B. anthracinus normally
hunts from a stationary perch, often near the
ground, from branches up to 15 m high, on boul-
ders, other low perches, and gravel beds along
streams. For Cuban hawks, Barbour (1923) de-
scribed crab predation similar to our observations:
“The hawk pounces on the crab, gathers the legs
and claws of each side in one of its feet, and reach-
ing down removes the carapace by hooking the bill
under its front edge.” Kirkconnell and Garrido
(1991) reported gundlachii drowning its avian prey
(Common Moorhen [Gallinula chloropus]), which
they suggested was unusual and perhaps related to
the abundant rain that caused the raising of the
water level in the swamp, rendering crabs difficult
to find.

We observed Cuban Black-Hawks caching crab
prey near their nest, a habit that has also been re-
ported for B. anthracinus in mainland sites (Thom-
as 1908, Schnell 1991, 1994).

As noted by Schnell (1994), descriptions of the
vocal behavior of Buteogallus anthracinus have been
confusing and conflicting. Schnell (1994) charac-
terized the common call (= alarm call) as of a
complex, un-raptor-like quality. The common call
of mainland Buteogallus anthracinus is distinct from
the three-note call of gundlachii, consisting of 9-24
notes (Reynard and Garrido 1988, Schnell 1994)
(Figs. 2A, 2C— F, Table 5). Similarly, the common
call of B. subtilis is distinct from that of gundlachii,
consisting of several, rapidly-repeated elements,
described by Ferguson-Lees and Christie (2001) as
a series of shrill whistles, indistinguishable from
that of anthracinus. The call of Buteogallus aequinoc-
tialis is a series of six or seven whistle-like notes,
the first three rapid, followed by slower and de-
scending elements (Fig. 2H; Ferguson-Lees and
Christie 2001). Finally, B. meriodionalis has a call
consisting of a prolonged whistle, described as

“eeeeee-eh” or ''kree-ee-ee-er” (Ferguson-Lees and
Christie 2001).

Conclusions

We consider Buteogallus anthracinus (with its geo-
graphical races, cancrivorus and anthracinus), B.
urubitinga, B. aequinoctialis, and B. gundlachii as sep-
arate species. This treatment of the Cuban popu-
lation agrees with Wetmore (1965:234), who stated
the other forms stand apart: “. . . from the bird of
the island of Cuba which it appears appropriate to
treat as a separate species, Buteogallus gundlachii.”
Thus, the Cuban Black-Hawk Buteogallus gundlachii
Cabanis, 1854 (1855), becomes a species endemic
to Cuba, distributed in the main island, where it is
relatively uncommon and quite localized, Isla de
Pinos, and many of the keys of the Cuban Archi-
pelago.

Acknowledgments

A grant from the American Museum of Natural History
allowed Garrido to undertake studies of West Indian
birds in its and other United States Museums. We grate-
fully acknowledge help and support from the RARE Cen-
ter for Tropical Conservation, through John Guarnaccia
and Victor L. Gonzalez, enabling visits to collections in
several museums. We also thank the curators of the
American Museum of Natural History, the Smithsonian
Institution, the Museum of Comparative Zoology, Loui-
siana State University Museum of Natural History, Acad-
emy of Natural Science, Delaware Museum of Natural
History, Instituto de Ecologia y Sistematica, and Museo
Nacional de Historia Natural de Cuba for their cooper-
ation. Wiley’s research in Isla de Pinos was supported by
grants from Wildlife Preservation Trust International,
World Parrot Fund, International Crane Foundation, and
the U. S. Department of the Interior. We are particularly
grateful to Lie. Xiomara Galvez, Empresa Nacional para
la Conservacion de la Flora y Fauna, for logistical support
and field assistance at Los Indios. For use of tape record-
ings of Buteogallus vocalizations, we thank George B. Rey-
nard, Paul Schwartz, L. Irby Davis, R. Grimshaw, J
Schnell, Richard Ranft, and the British Library Sound
Archive. We thank Lloyd F. Kiff, Jay H. Schnell, and an
anonymous reviewer for their helpful suggestions, which
greatly improved the manuscript.

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Aldrich, J.W. and B.P. Bole, Jr. 1937. The birds and
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Nat. Hist. 7:1-196.

Amadon, D. 1961. Remarks on the genus Buteogallus. Nov
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Received 28 June 2004; accepted 28 July 2005

Associate Editor: Cheryl R. Dykstra

J. Raptor Res. 39(4):365-377
© 2005 The Raptor Research Foundation, Inc.

HOME RANGE AND HABITAT USE OF NORTHERN SPOTTED
OWLS ON THE OLYMPIC PENINSULA, WASHINGTON

Eric D. Forsman,i TimmothyJ. Kaminski,^ Jeffery C. Lewis,^ Kevin J. Maurice,^ and

Stan G. Sovern^

USD A Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis, OR 97331 US. A.

Cheron Ferland and Elizabeth M. Glenn

Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331 US. A.

Abstract. — ^We studied movements and habitat selection of 20 adult northern Spotted Owls (Strix oc-
cidentalis caurina) on the Olympic Peninsula, Washington in 1987-89. Median annual home range size
of individual owls was 1147 ha based on the 75% isopleth of the Fixed Kernel (FK), 2406 ha based on
the 95% FK, and 2290 ha based on the 100% Minimum Convex Polygon (MCP). Annual ranges of
individual owls tracked >1 yr overlapped by a mean of 70-73%, depending on which estimator was
used. Size of annual and cumulative ranges was negatively correlated with the amount of old forest
within the cumulative MCP home range and within a 4.3 km radius of the center of activity. Overlap of
annual ranges of owls that were paired averaged 64 ± 5% based on the MCP and 69 ± 5% based on
the 95% FK. On average, ranges used during the nonbreeding season overlapped breeding season
ranges by 65.0 ± 4.5%, and breeding season ranges overlapped nonbreeding season ranges by 62.6 ±
4.9%. Compositional analysis of habitat selection indicated that old forests were the most preferred
cover type for foraging and roosting and that dear-cuts and non-forest cover types were rarely used.
There was little evidence that owls selected riparian areas or forest edges for foraging or roosting. Our
observations are consistent with the hypotheses that northern Spotted Owls use larger foraging areas
in regions where northern flying squirrels {Glaucomys sabnnus)arG their primary source of food, that
they prefer old forests for foraging and roosting, and that their home ranges become larger as the
amount of old forest declines. The large size of annual ranges on the Olympic Peninsula may be a
response to low prey biomass.

Key Words: Northern Spotted Owl, Strix occidentalis caurina; home range, habitat use, radiotelemetry, Olympic
Peninsular, Washington.

RANGO DE HOGAR Y USO DE habitat DE strix occidentalis CAURINA EN OLYMPIC PEN-
INSULA, WASHINGTON

Resumen. — Estudiamos los movimientos y la seleccion de habitat de 20 individuos adultos de Strix occi-
dentalis caurina en Olympic Peninsula, Washington, entre 1987 y 1989. La mediana del tamaho del area
de hogar de un individuo fue de 1147 ha basada en la isolinea de 75% del kernel fijo (KE), 2406 ha
basada en el 95% KF y 2290 ha basada en el 100% del poligono convexo minimo (PCM). Los rangos
anuales de los individuos seguidos por menos de un ano se superpusieron en promedio entre un 70%
y un 73%, dependiendo del estimador que usamos. Los tamanos de los rangos anuales y acumulativos
se correlacionaron negativamente con la cantidad de bosque maduro presente dentro del PCM acu-
mulativo del rango de hogar y a menos de 4.3 km del centre de actividad. La superposicion promedio
de los rangos de hogar anuales de individuos que confer maban parejas fue de 64 ± 5% basado en el
PCM y 69 ± 5% basado en el 95% del KF. En promedio, los rangos usados durante el periodo no
reproductive se superpusieron con los rangos del periodo reproductive en 65.0 ± 4.5%, y los rangos
del periodo reproductive se superpusieron con los rangos del periodo no reproductive en 62.6 ± 4.9%.

^ Email address: eforsman@fs.fed.us

^Present address: U.S. Forest Service, Bridger-Teton National Forest, P.O. Box 1888, Jackson, WY 83001 U.S.A.

^ Present address: Washington Department of Fish and Wildlife, 600 Capitol Way North, Olympia, WA 98501 U.S.A.

Present address: U.S. Fish and Wildlife Service, Portland Field Office, 2600 SE 98*, Portland, OR 97266 U.S.A.

’’ Present address: Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331 U.S.A.

365

366

Forsman et al.

VoL. 39, No. 4

Los analisis de composicion de los ambientes seleccionados indicaron que los bosques maduros fueron
el dpo de cobertura preferida para alimentarse y reposar, mientras que las areas completamente taladas
y no boscosas fueron usadas en muy pocas ocasiones. Encontramos muy poca evidencia de que las
lechuzas seleccionan las areas riparias o los hordes de bosque para alimentarse o reposar. Nuestras
observaciones son consistentes con la hipotesis de que S. o. caurina usa grandes areas de forrajeo en las
regiones donde las ardillas voladoras {Glaucomys sabrinus) son su fuente principal de alimento, que
prefieren bosques maduros para alimentarse y reposar y que sus areas de hogar aumentan a medida
que disminuye la cantidad de bosque maduro. El gran tamano de los rangos anuales en Olympic Pen-
insula podria responder a una baja biomasa de presas.

[Traduccion del equipo editorial]

Spotted Owls {Strix occidentalis) exhibit consid-
erable variation in home range size and patterns
of seasonal movements, both within and among re-
gions. For example, in some parts of their range,
Spotted Owls may migrate during winter, moving
16-58 km from their breeding season ranges into
lowland forests (Laymon 1989, Zabel et al. 1992).
In other regions, they are largely resident in the
same areas throughout the year (Forsman et al.
1984, Carey et al. 1990, 1992).

Home ranges and habitat selection of Spotted
Owls have been studied extensively in Oregon and
California, but with the exception of a study by
Hamer (1988), little information is available from
Washington. We examined home ranges and hab-
itat selection of northern Spotted Owls on the
Olympic Peninsula, Washington to determine if
patterns of habitat use differed near the northern
edge of the range of the owl compared to earlier
studies conducted in Oregon (e.g., Forsman et al.
1984, Carey et al. 1990, 1992, Carey and Peeler
1995) and northern California (Solis and Gutier-
rez 1990, Zabel et al. 1992, 1995).

Study Area

We conducted our study on two areas on the west side
of the Olympic Peninsula, one located 3 km SE of the
town of Forks, Clallam County, and the other located 10
km SE of the town of Quinault, Jefferson County (Fig.
1). Both areas were located on the Olympic National For-
est, had similar climate, topography and vegetation, and
will hereafter be referred to collectively as the “study
area.”

The study area was characterized by mountainous ter-
rain covered by forests of western hemlock (Tsuga hete-
rophylla) and western redcedar {Thuja plicata). Sitka
spruce {Picea sitchensis) was common on mesic, low ele-
vation areas, and Douglas-fir {Pseudotsuga menziesii) and
Pacific silver fir (Abies amabilis) were often intermixed
with western hemlock on upland sites (Henderson et al.
1986). Elevations ranged from 150-1500 m. Precipitation
ranged from 280-460 cm/yr, mostly falling as rain during
October-May.

The area included a mosaic of serai stages, ranging
from clearings in which all trees had been recently har-

vested (clear-cuts) to old-growth forests in which oversto-
ry trees were over 500 yr old (Henderson et al. 1986).
Approximately half of the area had been clear-cut within
the previous 30 yr, but harvested areas were not uniform-
ly distributed within the study area. Some areas were
heavily fragmented by recent clear-cuts, whereas other ar-
eas had extensive blocks of mature and old-growth forest.
Much of the study area was hit by hurricane-force winds
in 1921 which severely damaged many stands (Pierce
1921). As a result, many stands included a mixture of 60-
80-yr-old trees that regenerated after the wind event, in-
terspersed with old trees (80-500+ yr) that survived the
windstorm. All types of natural (unlogged) forest typical-
ly had high canopy closure (65-80%), high variation in
tree size and age, and high volumes of logs and snags
(Henderson et al. 1986). Regenerating stands of young
trees in clear-cut areas were usually even-aged, with high
canopy closure.

Methods

Capture and Radio-marking. We captured owls with
noose poles (Forsman 1983) and marked them with
back-pack transmitters (Model P2, AVM Instrument
Company, Livermore, CA U.S.A.), as described by Fors-
man et al. (1984). Total mass of transmitter and harness
was 18-20 g, and transmitter life was 9-15 mo. We tried
to obtain a minimum of 12 mo of data from each owl.
We replaced transmitters on six individuals after 9-12
mo, and tracked them for nearly 2 yr.

Sampling Schedule. We attempted to obtain one noc-
turnal foraging location per night on each owl at least 3
nights per wk, and one diurnal roost location per owl at
least 3 d per wk. Our sampling schedule was intended to
reduce autocorrelation between sequential locations
(Swihart and Slade 1985a, 1985b). However, Aebischer et
al. (1993) and Otis and White (1999) have suggested that
autocorrelation is generally irrelevant when individual
animals are used as the sample unit in home-range stud-
ies, so we used all of our data, including a few cases (129
of 7346 locations) when we obtained 2-3 locations on
the same owl in one night. We classified all locations as
foraging locations if they occurred from 0.5 hr after sun-
set to 0.5 hr before sunrise. We excluded locations of
incubating or brooding females from analyses of habitat
selection, until females began to forage when the young
were about 2 wk old.

Radio Triangulation. We estimated owl locations by tri-
angulating with a Telonics hand-held H-antenna and TR2
receiver (Telonics, Mesa, AZ U.S.A.). We used a hand-
held compass to estimate azimuths from ^3 locations

December 2005

Spotted Owl Habitat Use

367

Figure 1. Location of radiotelemetry study areas on the Olympic Peninsula, Washington, 1987-89.

)

along roads (Guetterman et al. 1991). Azimuths were
plotted on 1:12 000 or 1:24000 scale U.S. Geological Sur-
vey orthophotos or topographic maps. We considered the
position of the owl to be the geometric center of the
polygon formed by the intersection of ^3 bearings
(Nams and Boutin 1991). If weak signals or inconsisten-
cies in the direction of bearings caused us to suspect sig-
nal deflection or movement of an owl during triangula-
tion, we discarded the location. We used all locations to
estimate home ranges, but only locations with error poly-
gons ^8 ha were used for analyses of habitat use.

Telemetry Error. We estimated telemetry error with 63
blind trials in which one observer placed transmitters in
trees in owl home ranges and another observer then tri-
angulated on the transmitters at night. The median dis-
tance between estimated and actual transmitter locations
was 100 m (x = 140 ± 17 m). This estimate was similar
to or less than error estimates in previous telemetry stud-
ies of Spotted Owls (Carey et al. 1990, Glenn et al. 2004).
Errors of this magnitude undoubtedly resulted in some
locations falling in the wrong cover types, but we made
the assumption that classification errors due to telemetry
error were similar in all cover types, and that our overall
assessment should reflect actual habitat use.

Home-range Estimation. We estimated cumulative and
annual ranges with the Minimum Convex Polygon
(MCP) and Fixed-Kernel (FK) methods (Hayne 1949,
Seaman and Powell 1996). For estimates of MCP ranges,
we used 100% MCP polygons. For FK estimates, we used
95% and 75% isopleths, which we interpreted as the
“home range,” and “area of concentrated use,” respec-
tively. We used Program CALHOME (Kie et al. 1996) to
estimate MCP ranges and Version 4.28 of Program ICER-
NELHR (Seaman et al. 1998) to estimate FK ranges. Con-
trary to the recommendation of Seaman and Powell
(1996), we used the FK method without least-squares-
cross-validation (LSCV). We did so because we believe
that kernel estimates based on locations where owls stop
long enough for the observer to obtain a location tend
to underestimate home range areas of owls (because
movements across intervening non-forest areas usually
happen so quickly that they cannot be documented with
a point on the map) . Thus, we feel that the LSCV option,
which tends to fit the home range isopleth more tightly
to the observed points, is likely to cause an even greater
underestimate of home ranges. We used all locations for
MCP estimates, but we only used foraging locations for
FK estimates (because FK estimates that include large

368

Forsman et al.

VoL. 39, No. 4

Table 1. Vegetation cover types used to map landscapes for analyses of habitat use by northern Spotted Owls on
the Olympic Peninsula, Washington, 1987-89.

Old Forest: Multilayered stands of western hemlock and western redcedar in which the dominant overstory trees
were typically ^100 cm DBH. Pacific silver fir was often subdominant or codominant with hemlock or redcedar.
Douglas-fir was codominant on a few areas. Also included mixed-age stands of mature and old forest in which
both age classes were common. Many of the latter stands were the result of a hurricane force windstorm in
January 1921 (Pierce 1921).

Mature Forest: Conifer-dominated stands in which the overstory trees were typically 50—99 cm DBH.

Young Forest: Relatively even-aged stands in which most trees were 31-60 cm DBH. Regenerated on burned areas
and old dear-cuts.

Mixed-young Forest: Same as Young Forest except with inclusions of mature trees, usually remnants left during
previous fires or harvest.

Pole-sapling: Single-layered conifer stands in which most trees were 10-30 cm DBH. Mostly young stands regenerat-
ing on old dear-cuts.

Hardwood/Riparian: Riparian areas dominated by red alder {Alnus rubra), bigleaf maple {Acer macrophyllum) , and
variable amounts of western redcedar.

Clear-cut/Non-forest: Recent dear-cuts dominated by bare soil, grasses, shrubs or small seedling conifers. Also in-
cluded small areas of meadows, gravel pits, and agricultural, or residential areas.

numbers of roosting locations clustered at the nest site
or central place will underestimate foraging areas during
the breeding season) .

Estimation of Annual, Cumulative, and Seasonal Rang-
es, Although we marked some owls in June or July of

1987, we did not begin regular sampling of most individ-
uals until late July or August 1987, For these owls, we
estimated the first annual range through the end of July

1988. If they were monitored after July 1988, we com-
puted a second annual range for the second year. A few
individuals were not marked until fall 1987 or summer
1988, in which case the annual range was estimated for
one year only. There was only a weak positive correlation
between the number of days in the tracking period and
estimates of annual home-range size, regardless of which
home range estimator was used (95% FK r^^ ~ 0-221, P
= 0.223; MCP r^^ = 0.208, P = 0.253). Therefore, we
used all annual ranges for comparisons among owls, re-
gardless of the monitoring period.

For six owls tracked in both years, we estimated the
cumulative range from the union of the annual ranges
(range A -I- range B minus the area of overlap). Estimates
of home range overlap between years, seasons, pair mem-
bers, or owls on adjacent territories were based on the
percent of range A overlaid by range B or the percent of
range B overlaid by range A. In most cases, we computed
overlap of ranges based on three different frames of ref-
erence (75% FK, 95% FK, and 100% MCP). For estimates
of overlap of seasonal ranges, we only used the 95% FK.

For seasonal analysis of home ranges, we divided each
year into two phonological periods, the “breeding sea-
son” (March— August) , when Spotted Owls nest and feed
young, and the “nonbreeding season” (September— Feb-
ruary) , when Spotted Owls are largely solitary. Estimates
of seasonal ranges were limited to owls tracked sl20 d
during the season of interest.

Habitat Mapping and Assessment of Habitat Use. We
examined second-order habitat selection (i.e., use of dif-
ferent forest cover types within the home range of each

owl). We developed a cover-type map of the study area
that included seven cover types based on structural dif-
ferences in vegetation as determined from on-the-ground
examination of stands and aerial photo interpretation
(Table 1). We visited virtually all stands within the study
area on one or more occasions to determine the size and
species composition of trees. We did not use canopy clo-
sure to differentiate among cover types because nearly all
forests on the study area had relatively high (>70%) can-
opy closure, regardless of stand age or tree size. Cover
types were mapped on 1:12 000 scale orthophotos and
digitized into an ARC/INFO (ESRI Inc., Redlands, CA
U.S.A.) GIS layer. For convenience, we use the term cover
type, even though we recognize that our designation of
cover type was based on only one component of habitat
(i.e., vegetation structure). Site visits to 403 randomly se-
lected grid coordinates indicated tbat map accuracy was
83%.

We used compositional analysis (Aebischer et al. 1993)
to evaluate relative preference of cover types for foraging
and roosting. This method treats the individual as the
sample unit, accounts for lack of independence among
proportions, is not sensitive to serial correlation between
locations, and is based on a unique set of observed and
expected values for each cover type in the home range
of each individual. Expected use was equal to the pro-
portion of the cumulative MCP home range covered by
each cover type, and the observed use was the proportion
of locations in each cover type. We used Program RSW
(Leban 1999) to conduct the analysis. Results of this anal-
ysis included a numeric ranking of the different cover
types according to their relative “preference,” as well as
a table of pair-wise comparisons (Mests) indicating the
degree to which preference differed between types.

We used paired f-tests to determine if the distribution
of foraging or roosting locations differed from random
locations relative to elevation, distance to the nearest
stream, or distance to the nearest open area (dear-cuts/
non-forest in Table 1). For these analyses, we computed

December 2005

Spotted Owl Habitat Use

369

Figure 2. Observation periods of 20 radio-marked northern Spotted Owls observed on the Olympic Peninsula,
Washington, 1987-89. Vertical lines indicate intervals used for calculation of seasonal ranges.

mean expected values from a random sample of 200 lo-
cations in forest areas in the 100% MCP home range of
each owl. We used digital stream layers and elevation lay-
ers in GIS to compute elevation and distance to the near-
est stream for each owl location and each random loca-
tion.

Based on a preliminary analysis of our data, the Wash-
ington State Forest Practices Board (1996) adopted land
management guidelines in which they stipulated that
land managers should maintain a minimum of 5863 acres
(2372 ha) of “suitable habitat” within a 4.3-km radius
around Spotted Owl site centers (known or suspected
nest areas) on the Olympic Peninsula. To evaluate the
amount of protection afforded by these guidelines, we
examined the proportion of each cumulative owl home
range that fell within a 4.3-km radius of the nest area or
main roost area of each owl, and we compared median
and mean areas of “suitable habitat” in cumulative owl
ranges with the target in the Forest Practices Rules. All
means are expressed as x ± 1 SE.

Results

Sample Size and Tracking Periods. We moni-
tored 22 owls in 12 territories, including 10 resi-
dent pairs, one territory where we marked one
member of a resident pair, and one territory where
we marked an adult female that did not appear to
have a mate. We did not use the data from the
unpaired adult female because she did not exhibit
site fidelity. We also did not use data from one fe-
male that died shortly after she was radio-marked.

Of the 11 pairs in which one or both members
were radio-marked, three nested during the study,
including one pair in 1987 and two pairs in 1988.

On average, we tracked individual owls for 438
± 34 d (range = 166-711 d; Fig. 2). Total reloca-
tions per owl, not counting incubation locations,
averaged 366 ± 35 (range = 126-685). Of 3262
roost locations, we estimated 2360 (72%) by tri-
angulation and located 902 (28%) by homing in
on transmitters to locate owls visually in their roost
trees.

Annual Ranges. Median estimates of annual
ranges of individual owls were 1147 ha (75% FK),
2406 ha (95% FK), and 2290 ha (100% MCP; Table
2) . Most mean estimates of ranges were larger than
medians because means were skewed by a few in-
dividuals with large ranges (Table 2). All owls with
annual MCP or FK ranges >5000 ha were individ-
uals that expanded their ranges substantially dur-
ing fall and winter. Annual ranges were smaller for
females than for males, with the exception of the
75% FK estimate (Table 2). In six cases in which
we monitored owls for two yr, the sequential an-
nual ranges overlapped by 70 ± 6% based on the
75% FK (range = 18-100%), 73 ± 5% based on
the 95% FK (range = 27-100%), and 73 ± 4%
based on the MCP (range = 38-100%).

370

Forsman et al.

VoL. 39, No. 4

Table 2. Estimates of annual home-range areas of individual northern Spotted Owls on the Olympic Peninsula,
Washington, 1987-89. Estimates include the 100% minimum convex polygon (MCP) and the 75% and 95% isopleths
of the Fixed Kernel (FK) .

Number of Days and Number of Locations
IN Sample Period*^

Home Range Estimates (ha)

AND Year*

Days

Locations

75% FK

95% FK

100% MCP

BPF87

410

160

191

771

1696

1779

BPF88

116

2209

4196

3295

BPM87

386

147

180

1935

4865

6122

BPM88

325

144

145

3106

8469

8351

BRF87

302

136

415

1189

1402

BRF88

142

804

1720

1151

BRM87

373

172

532

1172

1367

BRM88

123

530

1045

683

ECF87

354

129

7927

15 212

10 704

ECF88

276

100

128

1404

4207

6668

ECM87

370

159

1108

2104

1917

ECM88

982

1876

1294

FBF87

166

1586

3483

3086

FBM87

206

106

1202

2411

2230

HRM88

366

201

186

2465

6924

7954

LBF88

345

137

143

2195

4931

4950

LBM88

391

168

184

1513

3232

3288

LCF88

246

109

967

2235

1915

LCM87

354

140

678

1504

2000

LCM88

509

1074

894

NRF87

387

133

174

734

1786

2350

NRF88

2597

5795

4537

NRF88

2597

5795

4537

NRM87

387

165

210

1186

3084

4284

NRM88

274

153

157

5003

11558

11252

RFF88

348

208

190

980

2092

2235

RFF89

114

554

1294

975

RFM88

309

152

144

2516

7059

6704

SPF87

396

154

169

468

1115

1323

SPF88

1228

2402

1406

SPM87

396

154

167

568

1583

1861

SPM88

247

151

142

1072

2533

3593

SRM87

314

2817

5693

3879

Mean

1642

3736

3608

Median

1147

2406

2290

Mean 9 ^

1656

3557

3185

Mean

1631

3893

3981

Median

967

2235

1915

Median d'*

1186

2533

3288

First two letters indicate owl name, third letter indicates sex of owl, and numbers indicate year of estimate.
Total locations for NRF87 and SPF87 also included 63 and 76 incubation locations, respectively.

TV = 1 6 owl years.

TV = 17 owl years.

December 2005

Spotted Owl Habitat Use

371

Table 3. Estimates of the cumulative home-range areas of northern Spotted Owls on the Olympic Peninsula, Wash-
ington, 1987-89. Estimates include the 100% minimum convex polygon (MCP) and the 75% and 95% isopleths of
the Fixed Kernal (FK) estimator.

Number of Days and Number of Locations
IN Sample Period

Owl Code
Name, Sex

Days

Roost

Locations

Forage

Locations

Home Range Estimates (ha)

75% FK 95% FK 100% MCP

BPF

526

226

261

2216

4303

3527

BPM

711

291

325

3235

8521

8715

BRF

444

194

804

1746

1562

BRM

496

209

645

1281

1372

ECF

630

172

257

7927

15212

10916

ECM

435

134

221

1215

2166

1932

LCM

449

182

845

1636

2026

NRF^

482

191

232

2580

5995

4852

NRM

661

318

367

5003

11561

11252

RFF

462

258

234

985

2164

2298

SPF^

482

202

224

1230

2436

1831

SPM

643

305

309

1090

2643

3716

Mean^

2315

4972

4500

Median*"

1222

2539

2912

Mean

2624

5309

4164

Mean

2006

4635

4836

Median 9'^

1173

3384

2912

Median

1152

2404

2870

^ Total locations for NRF and SPF also included 62 and 76 incubation locations, respectively.
bN = 12.

= 6.

Overlap of annual ranges of nine owls of the
same sex that occupied adjacent territories aver-
aged 5 ± 2% for the 75% FK (range = 0-25%),
21 ± 3% for the 95% FK (range = 3-58%), and
26 ± 4% for the MCP (range = 0-58%). These
estimates probably did not reflect total overlap
with adjacent residents because there were adja-
cent pairs that we did not have radio-marked and
because tracking periods for individual owls were
not always exactly the same. However, even with
incomplete data on some individuals and no data
on the pairs that were not radio-marked, it was
clear that home ranges of neighbors overlapped
considerably, particularly during winter. In one
case, a male from one territory (BPM) was found
on several occasions during winter, roosting in the
traditional nest area of an adjacent male (HRM) .

Cumulative Ranges. Median estimates of cumu-
lative ranges of individual owls monitored in two
sequential years were 1222 ha (75% FK), 2539 ha
(95% FK), and 2912 ha (MCP; Table 3). Cumula-
tive ranges of females averaged larger than cumu-

lative ranges of males for all comparisons except
the mean MCP (Table 3).

Seasonal Ranges. Ranges of individual owls
based on the 95% FK averaged 3360 ± 572 ha dur-
ing the breeding season (range = 883—10 205 ha,
median = 2052 ha, = 21) and 3175 ± 572 ha
during the nonbreeding season (range = 611-12
352 ha, median — 2168 ha, N = 29). There was no
consistent pattern of larger ranges in one season
or the other. Median estimates of seasonal ranges
were smaller than means because means were pos-
itively skewed by a few individuals with large rang-
es. Overlap of nonbreeding season ranges on
breeding season ranges averaged 65 ± 4.5%
(range = 8-98%, N= 36), and overlap of breeding
season ranges on nonbreeding ranges averaged 63
± 4.9% (range = 1-100%, N = 36). Overlap of
breeding season ranges of two owls tracked in two
different breeding seasons averaged 74 ± 8.9%
(range = 58-91%). Overlap of nonbreeding rang-
es of nine owls tracked in two different nonbreed-

372

Forsman et al.

VoL. 39, No. 4

Table 4. Results of compositional analysis of habitat use for foraging by northern Spotted Owls on the Olympic
Peninsula, Washington, 1987-89. Rank scores indicate relative preference of cover types from highest (6) to lowest
(0) . Results of pairwise t-tests indicate the relative preference of cover types. A positive lvalue indicates that the row
cover type ranked higher than the column cover type and a negative t-value indicates that the row cover type ranked
lower than the column cover type. A significant P-value suggests that confidence in the direction of the relationship
was high.

Cover Type^

Old

Forest

Mature

Forest

Mixed-

Young

Forest

Young

Forest

Pole-

sapling

Hard-

wood/

Riparian

Clear-

cut/Non-

forest

Rank

Old Forest

3.127

4.459

4.637

8.427

4.443

8.103

0.006

<0.001

Mature Forest

-3.127

-1.454

0.774

2.429

0.391

4.183

0.006

0.162

0.448

0.025

0.700

0.001

Mixed-young Forest

-4.459

1.454

2.756

6.676

2.743

6.528

<0.001

0.162

0.013

<0.001

0.013

<0.001

Young Forest

-4.637

-0.774

-2.756

1.561

-0.471

2.631

<0.001

0.448

0.013

0.135

0.643

0.017

Pole-sapling

-8.427

-2.429

-6.676

-1.561

-2.826

2.370

<0.001

0.025

<0.001

0.135

0.011

0.029

Hardwood/Riparian

-4.443

-0.391

-2.743

0.471

2.826

3.860

<0.001

0.700

0.013

0.643

0.011

0.001

Clear-cut/Non-forest

-8.102

-4.183

-6.528

-2.631

-2.370

-3.860

<0.001

0.001

<0.001

0.017

0.029

0.001

ing seasons averaged 59 ± 6.3% (range = 10-

100 %).

During the breeding season, movements of owls
were typically centered on the nest tree or, in the
case of nonnesting pairs, a regularly-used roost
area. Winter ranges typically included part of the
breeding-season range plus areas peripheral to the
breeding-season range. However, a few individuals
spent little time in their breeding-season ranges
during the winter season. The most dramatic ex-
ample was the Elk Creek Female (ECF) . After nest-
ing and producing a juvenile in 1987, she left the
nest area in August and spent most of the fall and
winter in an area 5-15 km away from the nest area
before eventually returning to the nest area in
June of 1988. The Neilton Ridge Male (NRM) also
had a very large nonbreeding range in 1988-89,
but in his case, the nonbreeding range overlapped
most of the breeding season range.

Ranges of Pairs. There were 14 cases where we
monitored annual ranges of paired owls in the
same year. The annual ranges of these pairs (union
of annual ranges of male and female) averaged
2397 ± 558 ha for the 75% FK (median = 1570
ha), 5449 ± 1111 ha for the 95% FK (median =
4081 ha), and 5414 ± 895 ha for the MCP (median
= 5032 ha). Overlap of annual ranges of paired

owls averaged 70 ± 5% based on the 75% FK
(range = 14-100%), 69 ± 5% based on the 95%FK
(range = 14—100%), and 64 ± 5% based on the
MCP (range = 14-100%). Estimates of mean over-
lap of annual ranges were similar, regardless of
which sex was used as the frame of reference, so
we based the above averages on all possible com-
binations of overlap.

Cumulative ranges of five pairs that were moni-
tored in both years averaged 3945 ± 1282 ha for
the 75% EK (median = 4053 ha), 8278 ± 2550 ha
for the 95% EK (median = 9329 ha), and 7488 ±
1951 ha for the MCP (median = 9195 ha). Overlap
of cumulative 95% FK ranges of paired individuals
averaged 68 ± 14% for males on females and 72
± 12% for females on males.

Habitat Selection. Use of cover types for forag-
ing and roosting was nonrandom. Old Forest was
the most preferred type for foraging, followed by
Mixed-young Forest, Mature Forest, Hardwood/Ri-
parian Forest, Young Forest, Pole-sapling, and
Clear-cut/Non-forest (Table 4). Pairwise compari-
sons of rank indicated that Old Forests were con-
sistently preferred over all other cover types (Table
4). Although Mixed-young Forest ranked higher
than Mature Forest, pairwise comparisons of rank
indicated little difference between the two types

December 2005

Spotted Owl Habitat Use

373

Table 5. Results of compositional analysis of habitat use for roosting by northern Spotted Owls on the Olympic
Peninsula, Washington, 1987-89. Rank scores indicate relative preference of cover types from highest (6) to lowest
(0) . Results of pairwise t-tests comparisons indicate the relative preference of cover types. A positive lvalue indicates
that the row cover type ranked higher than the column cover type and a negative f-value indicates that the row cover
type ranked lower than the column cover type. A significant P-value suggests that confidence in the direction of the
relationship was high.

Cover Type^*

Old

Forest

Mature

Forest

Mixed-

Young

Forest

Young

Forest

Pole-

sapling

Hard-

wood/

Riparian

Clear-

cut/Non-

forest

Rank

Old Forest

2.605

3.326

4.823

8.079

4.752

16.554

0.017

0.004

<0.001

Mature Forest

-2.605

0.121

1.141

5.124

1.361

10.527

0.017

0.905

0.268

<0.001

0.189

<0.001

Mixed-young Forest

-3.326

-0.121

1.163

5.195

1.711

9.010

0.004

0.905

0.259

<0.001

0.103

<0.001

Young Forest

-4.823

-1.141

-1.163

3.541

0.447

7.540

<0.001

0.268

0.259

0.002

0.660

<0.001

Pole-sapling

-8.079

-5.124

-5.195

-3.541

-3.271

2.543

<0.001

0.002

0.004

0.020

Hardwood/Riparian

-4.752

-1.361

-1.711

-0.447

3.271

6.477

<0.001

0.189

0.103

0.660

0.004

<0.001

Clear-cut/Non-forest

-16.554

-10.527

-9.010

-7.540

-2.543

-6.477

<0.001

0.020

<0.001

(Table 4). Similarly, Young Forest ranked lower
than Mature and Hardwood Forest, but pairwise
comparisons indicated that these differences were
weak (Table 4). Pole-sapling stands ranked lower
than all other types except Clear-cuts, but the pair-
wise comparisons with other types indicated that
preference for Pole-sapling was not greatly differ-
ent from Young Forest (Table 4). Large P-values
for all pairwise comparisons of Clear-cuts relative
to other cover types indicated that Clear-cuts were
the least preferred cover type for foraging. In fact,
out of 3822 foraging locations where cover type
could be determined, only 57 (1.5%) occurred in
Clear-cuts or Non-forest areas, and we suspected
that some of these cases were due to telemetry or
mapping error.

Use of cover types for roosting indicated that
Old Forests were preferred over all other cover
types (Table 5) . Mature Forest ranked higher than
Mixed-young, Young Forest, and Hardwood/Ripar-
ian Forest, but pairwise comparisons of these types
indicated that differences among them were weak
(Table 5). Pole-sapling, Clear-cuts, and Non-forest
areas were rarely used for roosting. Of 902 roosts
located visually, none were located in Clear-cuts or
Non-forest. Of 2275 roosts located by triangulation
alone, and for which cover type was determined,

eight were in Clear-cuts or Non-forest types; we sus-
pected these were due to triangulation or mapping
error.

Habitat Use Relative to Forest Edges, Streams,
and Elevation. On average, foraging locations and
roost locations were closer to openings (233 ± 24
m, and 271.9 ± 33.0 m, respectively) than were
random locations (304 ± 34 m; borage ~ — 4.10, P
= 0.001, ^roost = -2.04, P = 0.055; - 20 owls).

However, the number of locations within 100 m of
an edge was similar between random locations and
foraging locations (28.4% vs. 33.5%) and random
locations and roost locations (28.4% vs. 29.9%), so
we concluded that there was little evidence that
owls either preferred or avoided forest edges for
roosting or foraging.

Mean elevations at foraging locations (315 ± 29
m) and roosting locations (322 ± 31 m) were
slightly lower than elevations at random locations
(354 ± 36 m; = -3.63, P = 0.002, W ^
— 3.09, P = 0.006, N — 20 owls). Mean distance to
the nearest stream was similar for foraging (98 ±
14 m), roosting (112 ± 19 m), and random loca-
tions (94 ± 10 m; ^forage — 0.73, P = 0.475, ~

1.75, P = 0.097, = 20 owls).

Landscape Composition and Home Range Size.
Size of annual ranges was negatively correlated

374

Forsman et al.

VoL. 39, No. 4

with the percent cover of older forest (cover types:
Old and Mature forest) in the cumulative MCP
range, regardless of whether the estimator was the
75% FK (rgi = -0.53, P = 0.002), 95% FK (r^i =
-0.59, P < 0.001), or MCP = -0.67, P <
0.001). Size of annual ranges was also negatively
correlated with the amount of older forest in a 4.3
km circle centered on the central place (75% FK
r3i - -0.34, P = 0.058; 95% FK - -0.40, P -
0.028; MCP = -0.46, P - 0.009).

Overlap of Management Circles with Home
Ranges. On average, a 4.3-km radius circle cen-
tered on the nest site or center of activity included
94 ± 2% of the annual 75% FK home range, 86 ±
4% of the annual 95% FK home range, and 83 ±
4% of the annual MCP range. For 12 owls tracked
in both years, average overlap of the 4.3-km radius
circle on the cumulative range was 99 ± 13% for
the 75% FK range, 79 ± 7% for the 95% FKrange,
and 76 ± 7% for the MCP range. The counter-
intuitive result in which overlap of the 4.3-km cir-
cle was lower on the 75% FK annual range than
on the 75% FK cumulative range occurred because
the estimates were based on different individuals.
If we defined “suitable habitat” as the cover types
that had the top three preference rankings based
on compositional analysis (cover types = Old, Ma-
ture, and Mixed-young Forest), then the mean
amount of suitable habitat within a 4.3-km radius
circle was 3105 ± 236 ha.

Discussion

Home Range Attributes. The large ranges ob-
served in our study suggest that biomass of suitable
prey for Spotted Owls is lower on the Olympic Pen-
insula than in western Oregon and northwestern
California, where home ranges tend to be smaller
(Forsman et al. 1984, Carey et al. 1990, 1992, Zabel
et al. 1995, Bingham and Noon 1997, Glenn et al.
2004) . We did not have data on total prey biomass
in our study area, but Carey et al. (1992) found
that flying squirrels, which are the primary prey of
Spotted Owls on the Olympic Peninsula, were rel-
atively uncommon on the peninsula compared to
western Oregon.

As in our study, Carey et al. (1990) and Glenn
et al. (2004) found that home range size of north-
ern Spotted Owls was inversely related to the
amount of old forest in the home range. This sug-
gests that Spotted Owls respond to decreasing
amounts of their preferred habitat by increasing
the size of their ranges to encompass more old for-

est. However, Zabel et al. (1995) found no corre-
lation between home-range size of Spotted Owls
and the proportion of the range covered by large
trees. Instead, they found that home-range size was
positively correlated with the proportion of flying
squirrels in the diet and negatively correlated with
the proportion of woodrats (Neotoma spp.) in the
diet. In our study area, the diet was dominated by
flying squirrels (Forsman et al. 2001), which tend
to be most abundant in old forests (Carey et al.
1992, Waters and Zabel 1995). This could explain
why home ranges in our study area became larger
as the amount of old forest declined. However, for
a central-place forager like the Spotted Owl, the
ability to increase the size of the home range and
still function as a part of the resident breeding
population is probably limited by energetic and so-
cial constraints (Carey et al. 1992).

In our study, annual home ranges of paired owls
typically overlapped by 50-80%. Similar estimates
were obtained in a number of other studies (Fors-
man et al. 1984, Carey et al. 1990, Glenn et al.
2004). Our estimates of mean overlap of annual
ranges of owls on adjacent territories were higher
than values reported by Forsman et al. (1984:23;
MCP overlap = 12%) and Glenn et al. (2004:41;
95% FK overlap = 14.9 ± 4.3% and 6.7 ± 2.2%
on two different study areas) .

Habitat Selection. Our study, and most other
studies in which telemetry methods have been
used to examine habitat selection by northern
Spotted Owls, indicated that, given a choice, most
individuals selectively used older forests for forag-
ing and roosting and that younger stands generally
provided lower quality habitat (e.g., Forsman et al.
1984, Call 1989, Carey et al. 1990, 1992, Solis and
Gutierrez 1990, Gutierrez et al. 1995). However,
there have been two radiotelemetry studies of
northern Spotted Owls in landscapes dominated
by young forest, where patterns of habitat selection
were less clear. Glenn et al. (2004) examined hab-
itat selection by Spotted Owls in young forests in
northwest Oregon and did not find strong selec-
tion for any cover type. In a landscape where old
forest comprised less than 10% of the available cov-
er, Irwin et al. (2000) found that northern Spotted
Owls infrequently used stands <25 yr of age and
foraged primarily in mid-age stands (25—79 yr old)
or in remnant patches of old forest. However, Ir-
win et al. (2000) did not conduct a landscape-level
analysis of use-versus-availability with their data, so

December 2005

Spotted Owl Habitat Use

375

we could not determine if use of different cover
types differed from availability.

California Spotted Owls (5. o. occidentalis) in the
Sierra Nevada Mountains tended to forage in for-
ests with ^40% canopy cover, but did not show a
strong preference relative to tree age or tree size
(Zabel et al. 1992). However, at two of the three
study areas described by Zabel et al. (1992), the
majority of foraging and roosting locations were in
stands dominated by large (>53 cm DBH) trees.

Of the 5-6 species of small mammals that com-
prise the primary diet of Spotted Owls, several ap-
pear to be most abundant in older forests. For ex-
ample, there are a number of studies that suggest
that red tree voles {Arborimus longicaudus) and red-
backed voles {Clethrionomys californicus) are most
abundant in older forests (Corn and Bury 1986,
Aubry et al. 1991, Rosenberg et al. 1994). While
not all studies of northern flying squirrels have
found significantly higher numbers in old forests,
the trend in most studies was toward higher num-
bers in old forests (Carey et al. 1992, Rosenberg
and Anthony 1992, Waters and Zabel 1995, Lehm-
kuhl et al. (in press). Therefore, an obvious hy-
pothesis is that differences in abundance of pre-
ferred prey cause northern Spotted Owls to select
for older forests (Forsman et al. 1984, Carey et al.
1992). Ward et al. (1998) posed a similar hypoth-
esis to explain high use of forest edges by Spotted
Owls in northwestern California, where the diet
was dominated by dusky-footed woodrats {N. fusci-
pes), which were most abundant in brushy open-
ings adjacent to forests. In contrast, in areas where
they feed mainly on flying squirrels. Spotted Owls
either avoid non-forest edges or use them in pro-
portion to availability (Zabel et al. 1995, Glenn et
al. 2004, this study).

Streams and Elevation. Although Glenn et al.
(2004) found evidence that Spotted Owls foraged
selectively in riparian vegetation, we found no ev-
idence that foraging or roosting locations were
closer to streams than were random locations. We
concluded that there was no evidence from our
data that owls were either selecting or avoiding ri-
parian areas. Although Spotted Owls in our study
foraged at lower elevations than expected, the
mean difference between observed and expected
foraging locations was only 39 m. We were not con-
vinced that this relatively small difference was bi-
ologically meaningful.

Management Implications, Based on the results
of our study, we agree with Forsman et al. (1984),

Thomas et al. (1990), and Carey et al. (1992) that
management for northern Spotted Owls in western
Washington and Oregon should focus on the re-
tention of old forests. Although Franklin et al.
(2000) and Olson et al. (2004) found that north-
ern Spotted Owls may have higher reproductive
output in landscapes that include a mixture of old
forest and edges with other forest types, those stud-
ies were conducted in areas where woodrats were
a primary prey, and the results may not apply to
areas like the Olympic Peninsula, where flying
squirrels are the primary prey.

Bingham and Noon (1997, 1998) suggested that
the U.S. Fish and Wildlife Service should focus on
the most heavily-used portion of the home range,
or “core area,” as the frame of reference for as-
sessment of “take” of Spotted Owls. If this ap-
proach is used on the Olympic Peninsula, then we
believe it would be reasonable to use our estimates
of the 75% isopleth of the FK annual range as the
criteria for estimates of core areas, although other
methods have been proposed (Bingham and Noon
1997). We agree with Bingham and Noon (1997)
that it makes sense to use repeatable measures of
home range areas as the frame of reference for
assessments of “take,” but this should not be mis-
construed as a recommendation to manage Spot-
ted Owls based only on core areas. If the objective
is to provide Spotted Owls with enough habitat to
survive and reproduce on a site, then we agree with
Buchanan et al. (1998) that management should
be based on amounts of habitat within the entire
home-range areas of radio-marked owls, not just
core areas.

Our estimates of the median and mean amounts
of “suitable habitat” within cumulative MCP rang-
es of Spotted Owls (1824 ha and 2253 ± 286 ha)
are similar to or slightly lower than the manage-
ment target adopted by the Washington State For-
est Practices Board (1996) for management
around Spotted Owl nest sites (2373 ha of suitable
habitat within a 4.3-km radius). We found that a
4.3-km radius circle centered on the nest site en-
compassed about 83-87% of the mean cumulative
home range used by individual Spotted Owls on
the peninsula. Based on these results, we see no
reason to suggest changes to the 1996 Forest Prac-
tices Rules (Washington State Forest Practices
Board 1996). However, it remains to be seen if
Spotted Owls will persist in areas where old and
mature forests are gradually replaced with less-pre-
ferred types that are also classified as “suitable.”

376

Forsman et al.

VoL. 39, No. 4

Acknowledgments

For help with data collection, we thank Duane Aubu-
chon, Bruce Casler, Sue Grayson, Martha Jensen, Pete
Loschl, Rich Lowell, Paul Radley, Doreen Schmidt, Margy
Taylor, and Joe Zisa. Housing and administrative support
was provided by the Olympic National Forest. Reviews of
the manuscript by Rocky Gutierrez, Martin Raphael, Dan
Varland, and Cindy Zabel were extremely helpful. This
study was funded by the U.S. Department of Agriculture
Forest Service, Pacific Northwest Research Station, Port-
land, OR U.S.A.

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Received 4 April 2003; accepted 30 August 2005

J Raptor Res. 39(4):378-385
© 2005 The Raptor Research Foundation, Inc.

FIRST-CYCLE MOLTS IN NORTH AMERICAN FALCONIFORMES

Peter Pyle'

The Institute for Bird Populations, P.O. Box 1436, Point Reyes Station, CA 94956 U.S.A.

Abstract. — I examined 1849 specimens of 20 North American Falconiform species to elucidate the
occurrence and nomenclature of partial first-cycle molts. As reported in the literature, American Kestrel
{Falco sparverius) and White-tailed Kite (Elanus leucurus) have relatively complete body-feather molts that
occur during the first fall; in the kite, this molt can also include up to all rectrices and 2-6 secondaries,
but no primaries — an unusual pattern for such partial molts in first-year birds. Evidence of partial first-
cycle molts was found in 16 of 18 other species (among Pandion, Haliaeetus, Circus, Accipiter, Asturina,
Buteo, Aquila, and Falco) for which such molts have not been previously elucidated. Maximum extent of
body-feather replacement among individuals of these 16 species varied from 5-50%. On the other hand,
most species showed evidence that this molt could be absent (11-100% of birds remaining in juvenile
plumage until commencement of the complete or near-complete prebasic molt that occurs during the
first summer) . I argue that these partial molts are best considered preformative molts (following Howell
et al. 2003) rather than “first prebasic” molts, as defined by Humphrey and Parkes (1959). Variation
in the extent and timing of preformative molts may reflect various constraints according to species-
specihc breeding, migrating, and foraging strategies. The apparent lack of function for this molt suggests
that ancestral Falconiformes exhibited a more extensive preformative molt, as found in related orders
of birds, but that this molt has since become vestigial, at least in the larger species.

Key Words: American Kestrel, Falco sparverius; White-tailed Kite, Elanus leucurus; preformative molt, hawks;

falcons.

MUDAS DEL PRIMER CICLO EN FALCONIFORMES NORTEAMERICANOS

Resumen. — Examine 1849 especimenes de 20 especies norteamericanas de Falconiformes para estable-
cer la ocurrencia y la nomenclatura de mudas parciales del primer ciclo. Como habia sido informado
en la literatura, Falco sparverius y Elanus leucurus presentan mudas relativamente completas de las plumas
corporales que tienen lugar durante el primer otono, aunque en E. leucurus esta muda puede tambien
incluir algunas o todas las rectrices y 2-6 secundarias pero ninguna primaria. Esto constituye un patron
poco usual de mudas parciales durante el primer aho de vida. Encontre evidencia de mudas parciales
en el primer ciclo en 16 de las 18 especies adicionales (en los generos Pandion, Haliaeetus, Circus, Accipiter,
Asturina, Buteo, Aquila y Falco) para las cuales no se habia determinado previamente la ocurrencia de
mudas de este tipo. El maximo grado de reemplazo de las plumas del cuerpo en los individuos de esas
16 especies vario entre el 5% y el 50%. Por otra parte, la mayoria de las especies mostraron evidencia
de que esta muda podria estar ausente, pues entre el 11% y el 100% de los individuos mantuvieron el
plumaje juvenil hasta comenzar la muda prebasica completa, o casi completa, que tiene lugar durante
el primer verano. Sugiero que estas mudas prebasicas deben considerase mudas preformativas (siguien-
do la terminologia de Howell et al. 2003) en lugar de “primeras mudas prebasicas”, como fueron
definidas por Humphrey y Parkes (1959). La variacion en la extension y en el momenta de ocurrencia
de las mudas preformativas podria reflejar distintos limitantes de acuerdo a las estrategias reproductivas,
de migracion y de forrajeo especificas de cada especie. La falta aparente de funcionalidad de esta muda
sugiere que los Falconiformes ancestrales exhibian una muda preformativa mas extensiva, como se ha
documentado en ordenes de aves relacionados, pero que esta muda se ha vuelto vestigial, al menos en
las especies de mayor tamaho.

[Traduccion del equipo editorial]

North American Falconiformes exhibit various most species, Juvenal plumage is reportedly re-
molt strategies during their first year of life. In tained until the first spring or summer (when a

year old) , at which point a complete or near-com-

plete prebasic molt commences, usually with the

^ Email address: ppyle@birdpop.org shedding of the innermost primaries in Accipitri-

378

December 2005

First-cycle Molts in Falconiformes

379

dae or the medial primaries in Falconidae (e.g.,
Miller 1941, Palmer 1988, Forsman 1999, Wheeler
2003). In American Kestrel (Falco sparverius) and
certain kites, by contrast, most to all Juvenal body
feathers are replaced during the first fall, well be-
fore molt of the primaries commences during the
following summer (Bent 1937, 1938, Parkes 1955,
Palmer 1988, Miller and Smallwood 1997).

For some species of Falconiformes, a limited
number of body feathers are reported to be re-
placed during the first fall, winter, or spring, prior
to the shedding of primaries during the first spring
or summer. For example, Wheeler (2003) reported
that in the Red-shouldered Hawk (see Table 1 for
scientific names), “the first prebasic molt begins
on the breast, then is noticeable on the back and
scapulars” before molt of primaries begins, and
Forsman (1999) reported that in the Northern
Harrier, “single body-feathers and tail-feathers may
be replaced from late winter” prior to the com-
plete molt the following May to October. Similar
limited molts in fall, winter, or spring have been
reported for Osprey (Bent 1937), Northern Gos-
hawk (Bent 1937, Dement’ev and Gladkov 1951,
Forsman 1999), Gray Hawk (Dickey and van Ros-
sem 1938, Wheeler 2003), and several species of
Falconidae (Cramp and Simmons 1980, Forsman
1999, Wheeler 2003).

Most authors consider this limited body-feather
replacement to be the initiation of the prebasic
molt at a year of age (hereafter, “first complete
molt”) rather than a separate molt; indeed, Wheel-
er (2003) even interprets the fall molts in first-year
American Kestrel and kites as part of the first com-
plete molt, terminating with the flight feathers the
following summer. This interpretation appears to
disregard the additional body molt that occurs in
one-year-old birds concurrent with flight-feather
molt in these species (Parkes 1955, Palmer 1988).
Herremans and Louette (2000), on the other
hand, document that such molts in certain Old-
World species of Accipiter are distinct from the first
complete molt.

Thus, there remains confusion about both the
occurrence of partial first-cycle molts in Falconi-
formes and whether or not body-feather replace-
ment in the first fall, winter, or spring should be
considered part of a separate partial molt or as the
initiation of the first complete molt. To investigate
the occurrence and extent of partial first-cycle
molts in Falconiformes, I examined 1227 speci-
mens of 20 North American species collected dur-

ing their first year (age == 0-12 mo), prior to ini-
tiation of primary molt, and 622 specimens
collected in their second year (12-24 mo old) or
later.

Methods

Specimens of Falconiformes were examined at the Cal-
ifornia Academy of Sciences (CAS), San Francisco, the
Museum of Vertebrate Zoology (MVZ), Berkeley, and the
National Museum of Natural History (USNM), Washing-
ton, DC. Specimens were collected throughout North,
Central, and South America, but all specimens repre-
sented species or subspecies exhibiting boreal breeding
cycles. Data are presented for 20 species with A s 16
first-year individuals examined (Table 1).

Specimens examined included birds collected during
their first year of life, prior to the shedding of primaries
during the first complete molt, and birds determined to
be in their second year of life. Age of first-year birds was
determined by plumage features (Palmer 1988, Wheeler
2003), the presence of indicative fault bars (Hammers-
trom 1967), tapered and relatively worn outer primaries
and rectrices, and absence of wear and color patterns
among flight feathers indicating previous molts. Birds in
their second year were aged by the presence of predefi-
nitive plumage in some species or the retention of Juve-
nal feathers during the first “complete” molt, particular-
ly among the lesser coverts, on the rump, or within the
secondaries (Wheeler 2003).

Each first-year specimen was examined carefully for re-
placed body feathers in patterns indicating molt. Body
molt in Falconiformes typically begins on the head and
throat and proceeds caudally (Palmer 1988, Wheeler
2003). Thus, feathers showing wear patterns suggesting
replacement in a caudal direction were assumed to have
resulted from molt rather than adventitious replacement
(e.g., after accidental loss). Replaced feathers were often
intermediate in color or patterning between those of
first-year and second-year birds (Fig. 1), facilitating their
identification. The proportion of newly-replaced body
feathers, to the nearest 5%, was estimated for each spec-
imen. Those showing <2.5% replacement were scored as
0%, further ensuring that birds with adventitiously re-
placed feathers were not included in the sample evincing
molt. All primaries, secondaries, and rectrices were also
examined for evidence of symmetrical replacement in-
dicating molt. Secondaries were numbered proximally
from the outermost (si) to the innermost (si 3 in most
species) feather.

Second-year birds were examined for uniformity of
feather generations, particularly in tracts for which par-
tial molts were detected in first-year birds. The goal of
this examination was to assess whether or not feathers
replaced during the first year, prior to initiation of pri-
mary molt, had been replayed for a second time during
the first complete molt.

Results

Partial First-year Molts in White-tailed Kite and
American Kestrel. I examined 22 specimens of

380

Pyle

VoL. 39, No. 4

Table 1. Proportion of individuals showing evidence of molt and maximum percent of body feathers replaced,
among specimens of 18 species of North American Falconiformes, during three time periods within the first year
Values represent sample size of specimens examined, proportion of individuals showing evidence of molt, and max-
imum proportion of body feathers replaced among individuals sampled.

September-November

December-February

March-

May

Species

Proportion

Molting

Maximum

Percent

Feathers

Replaced

Proportion

Molting

Maximum

Percent

Feathers

Replaced

Proportion

Molting

Maximum

Percent

Feathers

Replaced

Osprey {Pandion
haliaetus)

0.40

10%

1.00

20%

1.00

35%

Bald Eagle {Haliaeetus
leucocephalus)

0.12

0.60

30%

1.00

40%

Northern Harrier
{Circus cyaneus)

0.00

0.33

15%

0.44

50%

Sharp-shinned Hawk
{Accipiter striatus)

0.00

0.12

10%

0.31

45%

Cooper’s Hawk
{Accipiter cooperii)

0.08

10%

0.31

10%

0.64

10%

Northern Goshawk
{Accipiter gentilis)

0.00

Gray Hawk

{Asturina nitida)

0.00

0.14

0.33

10%

Red-shouldered Hawk
{Buteo lineatus)

0.45

10%

0.45

10%

0.00

Broad-winged Hawk
{Buteo platypterus)

0.00

Swainson’s Hawk
{Buteo swains oni)

0.57

10%

1.00

25%

0.86

40%

Red-tailed Hawk
{Buteo jamaicensis)

0.21

0.26

10%

0.37

20%

Ferruginous Hawk
{Buteo regalis)

0.13

0.50

0.60

10%

Rough-legged Hawk
{Buteo lagopus)

0.31

0.50

15%

1.00

10%

Golden Eagle

{Aquila chrysaetos)

0.17

0.22

1.00

Merlin {Falco
columbarius)

0.04

0.33

15%

0.50

50%

Gyrfalcon {Falco
rusticolus)

0.07

10%

0.42

30%

0.20

25%

Peregrine Falcon
{Falco peregrinus)

0.19

10%

0.46

25%

0.85

20%

Prairie Falcon
{Falco mexicanus)

0.29

15%

0.50

15%

0.89

20%

White-tailed Kite and 183 specimens of American
Kestrel collected between September and May of
their first year. A partial to complete body-feather
molt during the first fall was confirmed for all in-
dividuals of both of these species. Proportions of
replaced feathers indicated that, in both species,
this molt had completed or nearly completed by

December, with little or no additional molt taking
place during January-May, until initiation of the
first complete molt. Examination of six White-
tailed Kites and 15 American Kestrels undergoing
their first complete molt and 73 kites and 274 kes-
trels in definitive plumage (showing uniform body
plumage) confirmed that another complete body

December 2005

First-cycle Molts in Falconiformes

381

A B C D

Figure 1. Pigraent patterns on underpart feathers of
Cooper’s Hawks. A — Typical Juvenal feather; B — Forma-
tive feather replaced in September (CAS62145); C — For-
mative feather replaced in January (CAS33560); D — Typ-
ical definitive feather.

molt occurs in these species concurrent with the
flight-feather molt at a year of age.

In White-tailed Kite, 13 first-year individuals col-
lected between January and the initiation of the
first complete molt (with shedding of the inner-
most primaries) had replaced a mean 97.7% of
body feathers. All 13 kites had replaced at least
some lesser coverts (but no median coverts) and
the central two to all 12 rectrices {x = 6.9 feath-
ers) . In addition, five individuals were found that
had replaced 2-6 secondaries during the partial
molt, symmetrically on both wings and apparently
in the same sequence as observed in complete
molts, as determined from dines in wear. The two
specimens with the most extensive partial first-year
molts were collected in California: MVZ24493 (10
January) and CAS73280 (22 February), each with
100% of the body feathers, all 12 rectrices, and sl-
s2, s5, and sll-sl3 replaced. No primaries had
been replaced during this molt in any individual.

In American Kestrel, 92 individuals collected be-
tween their first January and the initiation of the
first complete molt had replaced a mean of 90.8%
of body feathers. The amount of feathers replaced
ranged from 40% of the body and no wing coverts
(CAS 73504 collected 26 April) to 100% of the
body feathers, all lesser coverts, and up to three
proximal median coverts, but no flight feathers
(several specimens).

First-year Molts in other North American Falco-
niformes. Evidence of body-feather replacement
prior to initiation of primary molt was recorded in
16 North American Falconiformes (all but North-
ern Goshawk and Broad-winged Hawk; Table 1).
Replaced feathers were observed primarily on the

back and breast (Fig. 2). Specimens collected in
fall and early winter had replaced some feathers
on the crown, throat, and upper back; whereas
many spring specimens had replaced larger scap-
ulars and some breast feathers, but had retained
most to all feathers of the crown, upper back, and
throat. Newly-replaced feathers on the underparts
tended to show patterns resembling Juvenal feath-
ers when molted in fall and definitive feathers
when molted in spring, with a clinal rate of pattern
change with time (Fig. 1). The seasonal timing at
which definitive characteristics in these feathers
were acquired appeared to vary, occurring during
the late fall and winter in some species (e.g., Sharp-
shinned Hawk, Red-shouldered Hawk, and Pere-
grine Falcon) and during the spring or later in oth-
ers (e.g., Swainson’s and Rough-legged hawks).

Extent of this molt showed substantial intraspe-
cific and interspecific variation (Table 1). Among
the 16 species showing these molts, the mean max-
imum recorded extent for all species combined
was 25.6%, varying from 5% in Golden Eagle to
50% in Northern Harrier and Merlin (Table 1).
Examples of specimens showing extensive body-
feather replacement included Northern Harrier
MVZ144731 (collected in March with 35% replace-
ment), Sharp-shinned Hawk MVZ99723 (May,
45%), Swainson’s Hawk CAS13889 (April, 40%),
Red-tailed Hawk CAS27181 (April, 20%), Rough-
legged Hawk MVZ173433 (December, 20%), and
Peregrine Falcon CAS73587 (December, 25%; Fig.
2). On the other hand, at least some individuals
(11-80%) of 12 species (or 11—100% of 14 species
when Northern Goshawk and Broad-winged Hawk
are included) collected in March-May showed no
feather replacement (Table 1), and six specimens
were recorded that had begun shedding primaries
during the first complete molt, but remained in
complete Juvenal body plumage. No first-year birds
of these 22 species showed symmetrical replace-
ment of any flight feathers prior to initiation of the
first complete molt.

Two replacement patterns according to season
were observed among these 16 species (Table 1,
Fig. 3). In Northern Harrier, Sharp-shinned, Coo-
per’s, Gray, and Ferruginous hawks. Merlin, and
Peregrine and Prairie falcons, molt had com-
menced in few birds in fall, some birds in winter,
and most birds in spring. In Osprey and Red-shoul-
dered, Red-tailed, and Rough-legged hawks, molt
had occurred in some birds in fall, appeared to be
suspended in many birds over winter, and was re-

382

Pyle

VoL. 39, No. 4

Figure 2. Dorsal and ventral aspects of a first-year Peregrine Falcon {F. p. anatum) collected 15 December in Cali-
fornia (CAS73587) showing evidence of 25% body-feather replacement during a preformative molt (see Discussion).
Formative feathers on the dorsum are bluish and barred, and formadve feathers on the underparts are unstreaked
(breast) and barred (belly and flanks) , resembling definitive feathers in these regions.

sumed or initiated in some birds in spring. The
patterns for Bald and Golden eagles, Swainson’s
Hawk, and Gyrfalcon appeared to be intermediate,
with molt occurring throughout the first year (Ta-
ble 1).

Feather-replacement Patterns in Second-year
Birds. Totals of 27 birds collected while undergo-
ing the first complete molt and 146 second-year
(12-24 mo-old) birds following completion of this
molt were examined, including at least six individ-
uals of all species in Table 1 , except for Gray Hawk,
Red-shouldered Hawk, and Merlin, for which sec-
ond-year and older individuals could not be distin-
guished. For the smaller species (including all fal-

cons) , there was no evidence that feathers replaced
during the first fall, winter, or spring had been re-
tained during the first complete molt. All 27 birds
undergoing this complete molt appeared to be re-
placing all body feathers (or most feathers in the
case of the larger species; see below). On second-
year birds that had completed body molt, all scap-
ulars as well as crown, back, and underpart feathers
were uniform in wear, reflecting a complete molt
within a relatively short time period. For the three
species mentioned above, examination of 75 birds
in definitive plumage (likely including second-year
birds) also showed no variation in feather wear. For
five of the larger species, Osprey, Bald and Golden

December 2005

First-cycle Molts in Falconiformes

383

Month

Figure 3. Proportion of individuals evincing body molt,
by month, in two species of North American Falconifor-
mes showing differing seasonal-replacement strategies.

eagles, and Red-tailed and Ferruginous hawks, var-
iation in wear among the body feathers precluded
confirmation that feathers replaced during the first
year were replaced again during the first complete
molt. In the two species of eagle, up to many Ju-
venal body feathers could be retained during the
first “complete” molt, so it is possible that feathers
replaced during the first year may also have been
retained during this molt.

Discussion

Traditionally, both the partial first-fall molts of
North American Kestrels and kites and the com-
plete molts of other 1-yr-old Falconiformes have
been considered the “first prebasic molts,” accord-
ing to the molt terminology of Humphrey and
Parkes (1959). However, Howell and Corben
(2000) suggested that the complete first prebasic
molts of most Falconiformes may be homologous
with the second prebasic molts of kestrels, kites,
and most other birds. Accordingly, Howell et al.
(2003) proposed a revised molt terminology for
the first cycle, redefining the prejuvenal molt as syn-
onymous with the first prebasic molt, the complete
molt at the end of the first molt cycle as the second
prebasic molt, and any inserted molts during the first
cycle as preformative molts.

Evidence of body-feather replacement during
the first year was found in 18 of 20 species exam-
ined and, for at least 15 species, the “first complete
molt” appeared to include those feathers replaced
during the first cycle. By definition (Humphrey
and Parkes 1959, Howell et al. 2003), the addition-
al body-feather replacement during the first year
should be considered separate, inserted molts; us-

ing the terminology of Howell et al. (2003), they
should be considered preformative molts followed
by the complete or near-complete second prebasic
molt at a year of age. Under the terminology of
Humphrey and Parkes (1959), the “first prebasic
molt” referred to the limited body-feather molt
during the first fall, winter, or spring of some in-
dividuals or species and to the complete molt at a
year of age in other individuals, even within species
(cf. Elanus caeruleus in Marchant and Higgins
1993), and presumed homology between individ-
uals and species was lost.

In the remaining two species. Northern Gos-
hawk and Broad-winged Hawk, evidence of prefor-
mative molts may have been missed in this study
due to low sample sizes, especially in spring. In-
deed, body-feather replacement during the first
year has been reported for Northern Goshawk
(Bent 1937, Dement’ ev and Gladkov 1951, Fors-
man 1999). A first-year Broad-winged Hawk (Slater
Museum of Natural History No. 2367) collected 1
June reportedly had replaced some breast feathers
(Clark and Anderson 1984), although this individ-
ual had initiated the second prebasic molt (D.
Paulson pers. comm.). It is possible that the con-
straints of migration may preclude the occurrence
of a preformative molt in Broad-winged Hawk;
however, substantial evidence of this molt was
found in the migratory Swainson’s Hawk. In gen-
eral, birds that migrate to the tropics or Southern
Hemisphere often display more extensive first-win-
ter molts, possibly due to more abundant and sta-
ble food resources and greater day-lengths with
which to forage (Myers et al. 1985, Pyle 1998).
Thus, preformative molts should be expected in
some Broad-winged Hawks. The evidence, there-
fore, suggests that preformative molts likely occur
in at least some individuals of all North American
Falconiformes.

Including the pattern of White-tailed Kite and
American Kestrel, three seasonal strategies of pre-
formative molt were identified. Consideration of
the ecology and life history of the species com-
prising each group revealed no evident explana-
tions for conditions or constraints leading to each
molt pattern. There appeared to be a slight phy-
logenetic component, with a majority of species
among Accipiter and Falco delaying preformative
molts until winter or spring (see Herremans and
Louette 2000) , whereas more species among Buteo
initiated preformative molts in fall. Northerly
breeding and wintering species also tended to

384

Pyle

VoL. 39, No. 4

show a greater amount of preformative molt in fall;
perhaps first-year birds of these species can take
advantage of abundant food resources in the fall,
but suspend molting during winter when food be-
comes scarce. Such variation might also be expect-
ed within species that show a wide latitudinal
breeding range. Within genera, smaller species (in-
cluding Mdiite-tailed Kite and American Kestrel)
generally showed higher proportions of birds molt-
ing a greater amount of feathers. This correlation
is expected based on the added energy required
to replace larger feathers (Lindstrom et al. 1993) ,
and may also be part of a signaling mechanism for
species more likely to undergo breeding in their
first year (Kemp 1999, Herremans and Louette
2000). Finally, species inhabiting open areas ex-
posed to higher amounts of UV radiation appeared
to undergo more extensive preformative molts.
However, there were exceptions to all of these pat-
terns, and it is likely that the extent and timing of
preformative molts in Falconiformes reflect various
constraints according to a complex combination of
species-specific, breeding, migrating, and foraging
strategies.

Replacement patterns by season indicate that
breast feathers and scapulars can be molted later
in winter or spring during preformative molts,
while juvenal crown, throat, and upper back feath-
ers had been retained, an unusual sequence of
feather replacement for Falconiformes (Palmer
1988, Wheeler 2003). This suggests a triggering
mechanism for the preformative molt, by which
body molt of some feathers is bypassed, resulting
in spring birds initiating molt at a later point in
the sequence. Thus, sequence as well as extent may
vary individually, depending on initiation date.
Similarly, hormonal processes controlling feather
pattern appear to develop clinally throughout the
first year (and sometimes beyond), resulting in de-
layed acquisition of definitive plumage that varies
m timing by species. In Swainson’s Hawk and
Crested Caracara ( Caracara cheriway ) , acquisition of
definitive plumage is delayed until the following
summer or later, resulting in identifiable second-
basic plumages, intermediate in pattern between
juvenal and definitive plumages (Wheeler 2003).
For the two eagle species, acquisition of definitive
plumage requires up to 4 or 5 yr to complete.

Within many species, the preformative molt ap-
pears to occur in only a proportion of individuals,
with some birds retaining full Juvenal plumage un-
til the second prebasic molt. Similar variation in

the preformative molt was found among Eurasian
Accipiters (Herremans and Louette 2000). Thus,
some individuals exhibit a “Simple Basic Strategy”
(lacking a preformative molt) whereas others ex-
hibit a “Complex Basic Strategy ” (including a pre-
formative molt, but lacking prealternate molts) ac-
cording to Howell et al. (2003). However, at the
species level, Falconiformes are best described as
exhibiting the Complex Basic Strategy, with the
preformative molt ranging in extent from absent
to partial.

Evolutionarily, the existence of these variable
and at times ephemeral preformative molts may
suggest that ancestral Falconiformes exhibited
more extensive preformative molts that have be-
come vestigial in most (larger) species that do not
breed at age one and can commence the second
prebasic molt at an earlier age (Wheeler 2003).
Phylogenetic evidence suggests that ancestral Fal-
coniformes branched from a common ancestor
that also included Podicipediformes, Pelecanifor-
mes, and Ciconiformes (Sibley and Ahlquist 1990),
orders which currently display extensive prefor-
mative molts (Palmer 1962, Howell et al. 2003).
Alternatively, it is possible that these preformative
molts in Falconiformes have become inserted over
time, from an ancestral species that lacked such
molts; however, the apparent lack of functionality
for these molts may argue against this alternative
hypothesis. A better understanding of molt and
plumage homologies in Falconiformes awaits fur-
ther study of both molts and phylogenetic relation-
ships.

Acknowledgments

I thank Jack Dumbacher and Douglas J. Long (CAS),
Carla Cicero (MVZ), and James Dean (USNM) for access
to collections under their care and Dennis Paulson of the
Slater Museum of Natural History, Puget Sound, WA, for
examining a specimen of Broad-winged Hawk for me.
The manuscript benefited from comments by Steve N.G.
Howell, Christopher W. Thompson, William S. Clark, Jo-
sef K. Schmutz, and Marc Herremans. Funding for the
study of molts and plumages was provided by the Neo-
tropical Migratory Bird Conservation Act (grant No
2601) administered by the U.S. Fish and Wildlife Service.
This is Contribution No. 232 of The Institute for Bird
Populations.

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Received 12 Eebruary 2004; accepted 6 June 2005

Associate Editor: Ian G. Warkentin

J Raptor Res. 39(4) :386— 393
© 2005 The Raptor Research Foundation, Inc.

MORPHOMETRIC ANALYSIS OF LARGE FALCO SPECIES AND
THEIR HYBRIDS WITH IMPLICATIONS FOR CONSERVATION

Chris P. Eastham^

National Avian Research Centre, The Falcon Facility, Penllynin Farm, College Road,

Carmarthen, Wales SA33 5EH United Kingdom

Mike K. Nicholes^

Ecology Research Group, Canterbury Christ Church University College, Canterbury, Kent, CTl IQU United Kingdom

Abstract. — Morphometric examination of several large falcon species and their hybrids was conducted to
ascertain whether phenotype was an accurate indicator of hybrid parentage. Six external body measure-
ments were recorded from 167 Gyrfalcons {Falco rusticolus), Saker {F. cherrug). Peregrine (F. peregrinus),
and New Zealand Falcons {E novaezeelandiae) and from 100 FI, F2, and backcross hybrids of these species.
Principal Component Analysis separated pure species and also indicated clusters for FI peregrine X saker,
gyr X peregrine, and gyr X saker hybrids. Gyr X peregrine hybrids were distinguishable from their parent
species, but it was impossible to discriminate accurately between a complex (FI, F2, and backcross) of gyr
X saker hybrids and between these and the parent species. Escaped or released falconry hybrids are
perceived as a significant threat to the conservation of wild falcon populations. Under current legislation,
gyrs and their hybrids are CITES Appendix I species, and sakers are Appendix II species. We suggest that
phenotypic characteristics are not reliable for identification of such hybrids for legal purposes. Further-
more, analysis of measurements also identified a “paternal effect,” whereby Fj hybrids, irrespective of
gender, were phenotypically more similar to their paternal than their maternal progenitors.

Keywords: Peregrine Falcon', Falco peregrinus; Gyrfalcon-, Falco rusticolus; Saker Falcon-, Falco cherrug; New

Zealand Falcon', Falco novaezeelandiae; Falcon hybrids, morphometric, principal component analysis:, PCA; CITES.

anAlisis morfometrico de las especies de ealco de tamano grande y de sus

HIBRIDOS, E IMPLICACIONES PARA LA CONSERVACION

Resumen. — Se analizo la morfologia de varias especies de halcones y de sus hfbridos para averiguar si
el fenotipo es un indicador precise de la paternidad de los hfbridos. Se registraron seis medidas cor-
porales para un total de 167 individuos pertenecientes a las especies Ealco rusticolus, F. cherrug, E peregrinus
y E novaezeelandiae, y para un total de 100 hfbridos FI, F2 y retrocruces de estas especies. Un analisis
de componentes principales separo a las especies puras e identified grupos formados por hfbridos FI
E peregrinus X E. cherrug, E rusticolus X E peregrinus y E. rusticolus X E cherrug. Los hfbridos F. rusticolus X
F. peregrinus se diferenciaron de las especies parentales, pero fue imposible distinguir claramente entre
un complejo (FI, F2, retrocruces) de hfbridos F. rusticolus X F. cherrug, y entre este complejo y las
especies parentales. Los halcones hfbridos de cetrerfa que escapan o son liberados se consideran una
amenaza para la conservacidn de las poblaciones silvestres. Bajo la actual legislacidn, F. rusticolus y sus
hfbridos estan registradas en el Apendice I de CITES y F. cherrug en el Apendice II. Consideramos que
las caracterfsticas fenotfpicas no son confiables para la identificacidn de estos hfbridos con propdsitos
legales. Ademas, el analisis morfometrico identified “efectos paternos,” en donde los hfbridos FI, in-
dependientemente de su sexo, fueron fenotfpicamente mas similares a sus progenitores paternos que
a los maternos.

[Traduccidn del equipo editorial]

^ Present address: Klumpstugevagen 1, 61892 Kolmarden,
Sweden.

^ Corresponding author’s address: LEAP, University of
Greenwich at Medway, Chatham Maritime, Kent ME4
4TB, United Kingdom. Email: M.Nicholls@gre.ac.uk

One of the first domestic hybrid falcons was pro-
duced in 1971 from a female Saker Falcon {Falco
cherrug and male Peregrine Falcon {F. peregrinus,
Morris and Stevens 1971, Morris 1972). Since then,
falconers and raptor breeders have produced many
different hybrids from members of the Falconifor-

386

December 2005

Morphometrics oe Falcon Hybrids

387

Table 1. Identity of hybrid falcons used in the analysis.

Hybrid Identity^

Samples Sizes

Male Parent

Fkmat.f. Parent

FIs

Gyr X Peregrine

6 d, 7 9

Gyr

Peregrine

Gyr X Saker

7 c?, 5 9

Gyr

Saker

Peregrine X Saker

3 c?, 13 9

Peregrine

Saker

Peregrine X Gyr

1 c?

Peregrine

Gyr

Peregrine X New Zealand

1 d

Peregrine

New Zealand

Gyr/Saker X Peregrine

1 d, 1 9

Gyr X Saker F2 hybrid

Peregrine

F2s

Gyr X Saker

4 d, 5 9

Gyr X Saker FI hybrid

Backcrosses — 1st generation

Gyr X Gyr/Saker

3 d, 1 9

Gyr

Gyr X Saker FI hybrid

Saker X Gyr/Saker

3 d, 3 9

Saker

Gyr X Saker FI hybrid

Gyr/Saker X Saker

14 d, 17 9

Gyr X Saker FI hybrid

Saker

Gyr/Peregrine X Peregrine

2 d

Gyr X Peregrine FI hybrid

Peregrine

Backcrosses — 2nd generation

Gyr (3/8)VSaker

1 d

Gyr X Saker FI hybrid

Gyr/Saker X Saker

(backcross hybrid)

Gyr (5/8)VSaker

1 d, 1 9

Gyr

Gyr/Saker X Saker

(backcross hybrid)

® When naming hybrids, the paternal species is cited first. For example, a cross between a male gyr and female saker is a gyr X saker
(or gyr/ saker) hybrid, whereas a male saker crossed with a female gyr is a saker X gyr (saker/ gyr) hybrid.

These numbers represent a simple way to show the proportion of genes from the parent species, assuming that a FI hybrid inherits
Vz of the genes from both the male and female parent species. For example, a gyr (%) /saker, produced by backcrossing a gyr X saker
FI hybrid with a gyr/ saker backcross hybrid, has \ gyrfalcon and \ saker genes.

mes (Boyd and Boyd 1975, Cade and Weaver 1976,
Bunnell 1986, Weaver and Cade 1991), including
intergeneric hybrids (e.g., Harris’s Hawks {Para-
buteo unicinctus] X Cooper’s Hawk [Aedpiter coope-
ni\ and Harris’s Hawk X Ferruginous Hawk {Buteo
regalis] ; Fox and Sherrod 1999a) for falconry pur-
poses.

Many Fj hybrids are fully viable (Heidenreich
1997), in their turn producing Fg hybrids or back-
crosses (Bj and B^ representing 1st and 2nd gen-
eration backcrosses) to one or other parent spe-
cies. Indeed, hybrids from within the subgenus
Hierofalco, the “desert falcon” group (Heidenreich
1997), exhibit full fertility, presumably over indef-
inite generations. Less closely-related pairs of spe-
cies, such as gyr (F. rusticolus) and peregrine, pro-
duce hybrids with reduced fertility, manifest as
deformed spermatozoa, completely sterile females
(Heidenreich and Kuspert 1992), or unviable em-
bryos (Rosenkranz 1995).

This extended viability of some falcon hybrids
coupled with increasing demand over the last 10
yr for domestic falcons from North American, Eu-

ropean, and Arabian falconry markets (Fox and
Sherrod 1999b) has prompted conservation con-
cerns. Escaped domestic hybrids may be merely a
curiosity (Forseman 1999), a nuisance for bird
watchers (Gantlett and Millington 1992), or a
threat to the integrity of wild populations. Indeed,
falcon pairs made up of an escaped hybrid and a
wild, pure individual have been documented sev-
eral times (e.g., Kleinstauber and Seeber 2000,
Lindberg 2000) . A further conservation issue pre-
sumably concerns illegal-trade in falcons, whereby
protected falcon species may be “laundered” as
domestic hybrids. In this study, we examine the re-
lationship between falcon species and their hy-
brids, particularly the accuracy of using morpho-
metric characters for identification, and discuss the
conservation issues concerning falcon hybrids.

Methods

We investigated four large falcon species, namely Per-
egrine, Gyr, Saker, and New Zealand falcons {F. novaezee-
landiae) and several of their hybrid types used for falcon-
ry. Hybrid falcons were all bred in captivity and,
therefore, their parentage was known. Six external body

388

Eastham and Nicholls

VoL. 39, No. 4

Table 2. Principal Component Analysis (PCA) of six anatomical measurements from juvenile male Gyrfalcon, Saker,
Peregrine, and New Zealand falcon species and hybrids of those species. Eigenvalues and eigenvectors (based on the
correlation matrix).

Principai. Component

Eigenvalue

3.0328

1.3691

0.7459

0.6833

Percent of variability

0.5055

0.2282

0.1243

0.1139

Cumulated Percent

0.5055

0.7336

0.8580

0.9718

Characters

Eigenvectors

Wing chord

0.4990

-0.2324

0.1490

-0.3852

Wing width

0.5552

-0.0321

-0.0688

-0.1697

Tail length

0.5195

0.2308

-0.2347

-0.1471

Tail step

0.0247

0.6402

0.7536

-0.1395

Tarsus length

0.3536

0.3591

-0.1598

0.7769

Digit three length

0.2170

-0.5940

0.5697

0.4221

measurements were collected from live juvenile Gyrfal-
cons {N = 7 males and 6 females) , Saker {N = 34 males
and 40 females). Peregrine {N = 17 males and 24 fe-
males), and New Zealand falcons {N = 25 males and 14
females), and their various hybrids (Table 1). Apart from
European Peregrine Falcon subspecies, the majority of
which were F. peregrinus peregrinus, no other differentia-
tion was made between subspecies or geographic
morphs. All birds were kept at the National Avian Re-
search Center’s Falcon Facility in Carmarthen, Wales,
U.K. The majority of Fg and backcross 1 and 2 hybrids
were between gyrs and sakers. This is because hybrids
between members of the subgenus Hierofalco remain fer-
tile for an indefinite number of generations, whereas hy-
brids between more out-crossed falcon species, such as
peregrines and sakers, have a reduced fertility. Some of
the hybrids included are produced in very low numbers
(e.g., Peregrine Falcon X New Zealand Falcon), and pub-
lished data on these are rare. Therefore, we included
them in the analysis.

One of us (C. Eastham) took six measurements, name-
ly wing chord length and width, tail length, tail step (the
difference between the outermost tail feather [rectrix 6]
and the tip of the center tail feather [rectrix 1] on the
same side), tarsus length, and third digit length from
each bird. Measurement protocols followed standard
methods described by Baldwin et al. (1931), Fox (1977),
Biggs et al. (1978), Kemp (1987), and Fox et al. (1997).
Feather characters were measured to the nearest 1 mm
and non-feather characters to the nearest 0.1 mm using
a pair of digital calipers, a steel ruler, and tape measure.
Inclusion of single individuals, for example, a male Per-
egrine Falcon X New Zealand Falcon, allowed us to em-
ploy Principal Component Analysis (PCA) on XLSTAT-
Pro (Fahmy 1998) statistical software as a suitable method
for data analysis. Male and female data were analyzed
separately to eliminate background variation due to re-
versed sexual size dimorphism (Brown and Amadon
1968, Cade 1982), or other sex-linked or sex-limited char-
acters. We used wing chord length to distinguish males

and females, as this measurement was reported by Wyllie
and Newton (1994) and Eastham (2000) to be the most
reliable indicator of overall body size.

Results

Males. Principal Component (PC) 1 (Table 2,
Fig. 1) accounted for the majority (50.5%) of var-
iation. Because all eigenvectors for PCI showed
positive and nearly equal values, we concluded this
component represents overall body size (Wiley
1981). Male gyrs and FI and F2 gyr/saker hybrids
had the largest body size, whilst male peregrines
and New Zealand Falcons were the smallest.

PC 2 (Table 2, Fig. 1) accounted for 22.8% of
the variation, as indicated by a contrast in eigen-
vectors between the positively weighted tail step,
tail and tarsus length, the negatively weighted digit
three length, and wing chord length and width
(Table 2). This component summarizes variation
related to body shape. Tail step and digit three
length showed the strongest positive and negative
weightings, respectively. With a low negative
weighting, wing width was of limited use in further
analysis of PC 2. New Zealand Falcons had the rel-
atively longest tail step (indicating a more rounded
tail) , tail and tarsus length, and shortest digit three
and wing chord, whilst peregrines, the single per-
egrine X New Zealand hybrid and gyr/ saker X per-
egrine hybrid had the relatively longest digit three
and wing chord length and shortest tail step and
tail and tarsus length. FI gyr X peregrines and sa-
kers showed a wide variation in PC 2 values, with
an individual saker having the highest PC 2 value.

December 2005

Morphometrics of Falcon Hybrids

389

Principal Component 1

• Gyrfalcon BSaker JKPeregrine -New Zealand falcon AGyr/ Peregrine +Gyr/Saker- FI • Gyr / Saker - F2

X Peregrine / Saker A Peregrine / New Zealand ^ Gyr x Gyr/ Saker □ Gyr/ Saker x Saker OSakerx Gyr/ Saker :: Gyr (5/8) / Saker SSGyr/ Saker x Peregrine

Figure 1. Principal component scores from morphometric comparison of various male falcon species and their
hybrids.

PC 3 and 4 (Table 2) accounted for only 12.4%
and 11.3% of the residual variation, respectively.
Tail step and digit three length had a high positive
weighting in PC 3, and in PC 4, there was a con-
trast between positively weighted tarsus and digit
three length and negatively weighted wing chord
length. As PC 1 and 2 together accounted for the
majority (73%) of variation, we did not consider
PC 3 and 4 further.

Females. The PCA for juvenile female falcons
showed a similar pattern of variation as that seen
in juvenile males. Again PC 1 (Table 3, Fig. 2) ac-
counted for the largest proportion (44.7%) of var-
iation and as indicated by mostly positive and near-
ly equal values represents, as with males, overall
size (Wiley 1981). Gyrs and the various gyr/ saker
FI, F2 and backcrosses had the largest size, whilst
Peregrine and New Zealand falcons were the small-
est.

PC 2 (Table 3, Fig. 2) accounted for a further
21.8% of the variation, and we concluded that this,
again like males, was related to shape. This was in-
dicated by a contrast in eigenvectors between tbe

positively weighted tail step, tail and tarsus length,
the negatively weighted digit three length, and
wing chord length and width (Table 3). Positively
weighted tail step and negatively weighted digit
three and wing chord length had the highest ei-
genvectors for this PC. New Zealand Falcons had
the longest tail step and the shortest digit three
and wing chord length, whilst FI gyr X peregrines
and peregrines had the shortest tail length and the
longest digit three and wing chord length. PC 3
and PC 4 (Table 3) accounted for 18.4% and
11.4% of the variation, respectively. As for males,
we did not consider these principal components
further.

Discussion

Using PCA we found that the four falcon species,
irrespective of sex, were clearly separated into
groups: New Zealand Falcons with a small size,
long rounded tails and tarsi, and short wings; per-
egrines, also with a small size, long digit three
lengths, and long narrow wings; sakers with a large

390

Eastham and Nicholls

VOL. 39, No. 4

Table 3. Principal Component Analysis (PCA) of six anatomical measurements from juvenile female Gyrfalcon,
Saker, Peregrine, and New Zealand falcon species and hybrids of those species. Eigenvalues and eigenvectors (based
on the correlation matrix).

Principal Component

Eigenvalue

2.6826

1.3071

1.1023

0.6864

Percent of variability

0.4471

0.2179

0.1837

0.1144

Cumulated percent

0.4471

0.6649

0.8487

0.9631

Characters

Eigenvectors

Wing chord

0.4717

-0.3853

■0.1963

0.4118

Wing width

0.5765

-0.1767

■0.0356

-0.0129

Tail length

0.5737

0.1670

■0.0642

-0.1107

Tail step

0.0866

0.6865

0.1871

0.6869

Tarsus length

0.3077

0.2169

0.6899

-0.4484

Digit three length

-0.1177

-0.5236

0.6672

0.3809

size, long rounded tails, and short digits; and gyrs
with the largest size.

Using these external body measurements, we
also found it possible to identify three main hybrid
groups: a complex of FI, F2 and backcross gyr/
sakers; FI gyr X peregrines and FI peregrine X
sakers. Further, it was possible to separate gyr X
peregrines from their parent species, but impossi-
ble to separate completely the FI, F2, and back-
cross gyr/ sakers hybrid-complex from pure sakers
or particularly, from pure gyrs.

Overall, we found that the hybrids were gener-
ally of intermediate phenotype between their par-
ents. However, beyond this it appears that the pa-
ternal progenitor influences the phenotype to a
greater extent than maternal. For example, for
both males and females, the clusters representing
FI gyr X peregrine hybrids, hybrids whose male
parents were gyrs, were spatially closer to the gyr
clusters than to the peregrine clusters (Fig. 1, 2).
Thus, both male and female gyr X peregrine hy-
brids have a morphology closer to that of gyrs than
to peregrines. Further, that the single female per-
egrine X gyr, whose sire was a peregrine, was spa-
tially closer to the peregrine cluster than the gyr
cluster, adds further weight to this proposed gen-
erality. Similarly, the male and female FI gyr X sa-
kers, both with gyrs as male parent, appear more
gyr-like than saker-like in morphology. Except for
male FI peregrine X sakers this “paternal effect”
seems true for all species combinations. We ex-
plain this by considering that two thirds of the sex
linked genes in a population are carried by the

homogametic sex (male in birds; Mittwoch 1977)
and only one third by the heterogametic sex (Fal-
coner 1967). Therefore, falcon sires (the homo-
gametic sex) will contribute more sex-linked alleles
to their hybrid offspring than will (heterogametic)
dams.

International trade in endangered species, such
as some falcons, can be a profitable enterprise and,
if unregulated, can threaten their conservation.
Regulation of the trade in such endangered spe-
cies is by international agreements, such as the
Convention on International Trade in Endangered
Species of Wild Fauna and Flora (CITES). Accord-
ing to their degree of endangerment in the wild,
all species are classed in one of three CITES ap-
pendices. Special conditions apply to the most en-
dangered, known as Appendix I species (i.e., those
threatened with extinction and whose survival
could be impaired by trade) , which allows restrict-
ed trade in captive and domestic bred individuals.
Appendix II includes species considered less
threatened. The saker is an Appendix II species,
and although trade is regulated, this is less exact-
ing than for Appendix I species. Despite relatively
healthy world populations and for reasons which
are largely political (White and Kiff 1998), gyrs and
peregrines and their hybrids are included in Ap-
pendix I.

The results we present here show that it can be
difficult to discriminate falcon species accurately
from their hybrids, especially hybrids of Appendix
I gyrs and Appendix II sakers. Similarly, plumage
variation, especially in juvenile falcons, is difficult

December 2005

Morphometrics of Falcon Hybrids

391

• Gyrfalcon

■ Saker

)K Peregrine

- New Zealand falcon

A Gyr /Peregrine

+ Gyr /Saker - F1

• Gyr / Saker - F2

X Peregrine / Saker

>I< Peregrine / Gyr

<>Gyr X Gyr / Saker

A Gyr / Peregrine x Peregrine

□ Gyr / Saker x Saker

O Saker x Gyr / Saker

:: Gyr (5/8) / Saker

— Gyr (3/8) / Saker

SSGyr / Saker x Peregrine

Figure 2. Principal component scores from morphometric comparison of various female falcon species and their
hybrids.

to assess objectively and make comparisons be-
tween species and their hybrids. These observa-
tions may provide fuel for two separate arguments.

Ornithologists are increasingly aware of the
widespread genomic compatibility and potential
for hybridization amongst what appear to be very
dissimilar species (Grant and Grant 1992), such
that hybridization between avian species is consid-
ered more common than originally thought (Gill
1998). Mayr and Short (1970) estimated that up to
10% of North American bird species regularly hy-
bridize; it’s so common that hybrids are even in-
cluded in birdwatchers’ field guides (Sibley 2000).
The presence of natural hybrids is not believed to
be a threat to the integrity of a species, even
though they may challenge the biological species
concept of taxonomists (Brookes 1999). Amongst
free-living, wild birds of prey such hybridization is
increasingly documented at the subspecific (Fefe-
lov 2001), specific (Hamer et al. 1994), and even
to the intergeneric levels (Corso and Gildi 1998,
Yosef et al. 2001).

Introgressive hybridization may therefore be a
process by which species evolve, rather than some-

thing that will corrupt them. Thus, if the species
concept for birds is much looser than conservation
law dictates, then perhaps it is the legislation and
not the species concept that must be challenged.
For example, the so-called “Altai falcon” (Falco al-
taicus Menzbier) , whose phenotype seems to share
characters with both gyrs and sakers, is believed by
some to be the result of introgressive hybridization
between gyrs and sakers, rendering all these as
allospecies within a single superspecies (Pfander
1987, Ellis 1995a, 1995b). This being so, then to
discriminate between Appendix I gyrs and Appen-
dix II sakers may be irrelevant, and artificially pro-
duced crosses between these two may be of no evo-
lutionary threat should they escape to the wild. If,
however, the Altai Falcon is merely a large, dark
race of the saker (Eastham and Nicholls 2002) , and
any resemblance to gyrs is merely superficial, then
escaped hybrids between these species could po-
tentially compromise wild populations, and the in-
tegrity of gyrs and sakers must be recognized and
CITES regulations enforced.

A different view of the role of natural hybridiza-
tion accepts that avian species are dynamic entities.

392

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VoL. 39, No. 4

which in certain circumstances, freely exchange
genes with other such entities. Despite these inter-
actions, the integrity of the whole is a fragile one,
and to short circuit gene flow via artificial hybrids
is a danger to this integrity. CITES protocols are
the response to perceived conservation status, and
therefore, it should be mandatory to discriminate
between species as we know them. Accurate iden-
tification to assist in controlling the trade in fal-
cons is paramount, and we have shown that criteria
other than phenotypic characteristics (e.g., DNA
markers) must be employed to identify individuals
and species. This is imperative if CITES is to re-
main an effective means of regulating legitimate
trade and protecting species in the wild.

Acknowled gments

Thanks to His Highness Sheikh Khalifa bin Zayed A1
Nahyan and His Highness Sheikh Hamdan bin Zayed A1
Nahyan for sponsoring this research. Thanks also to M.
A1 Bowardi, managing director of the Environmental Re-
search and Wildlife Development Agency (ERWDA), Drs.
Nick Fox, Director of the ERWDA Falcon Programme,
Robert Kenward, and Juan Negro and Violeta Munoz for
comments on this manuscript.

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Former Associate Editor: Juan Jose Negro

/. Raptor Res. 39(4):394-403
© 2005 The Raptor Research Foundation, Inc.

A CHANGE IN FORAGING SUCCESS AND COOPERATIVE
HUNTING BY A BREEDING PAIR OF PEREGRINE FALCONS

AND THEIR FLEDGLINGS

Dick Dekker^

3819-112A Street NW, Edmonton, Alberta, T6J 1K4 Canada

Robert Taylor

P.O. Box 3105, Spruce Grove, Alberta, T7X 3A1 Canada

Abstract. — The foraging habits of one pair of Peregrine Falcons (Falco peregrinus) nesting on a power
plant in central Alberta were studied over seven consecutive breeding seasons (1998-2004) . We observed
386 attacks that resulted in II7 captures of prey. The success rate increased from 21.9% in the first year
to 39.1% in the seventh year and averaged 30.3%. The majority of hunts (76.7%) were initiated from
soaring, and the peregrines commonly used the hot air above the plant’s smoke stacks to gain height.
The success rates of hunts launched from soaring versus perches were not significantly different (28.7%
versus 35.6%). Tandem hunts by the pair {N = 100) were more successful than solo hunts (39.0% versus
27.3%), but the difference was not significant. The main prey species were Franklin’s Gull {Larus pipix-
can) and small passerines, which made up 53.0% and 27.4% of kills, respectively. There was a significant
difference in the respective capture rates of these prey types (42.5% versus 24.1%). The success rates
of the male and the female peregrines were not significantly different, but there was a notable difference
in the prey taxa taken by each gender. The male captured 84.4% of the passerines, but only 22.9% of
the gulls. After the first year, there was a significant switch from passerines to gulls, which paralleled a
significant change in gender participation in foraging. All gulls captured by the male were surrendered
to the female or to the fledged Juveniles. In 23.3% of hunts, one or both parents were accompanied
by one or more fledglings. The male participated in 76.7% of all parent-fledgling hunts {N = 90), the
female in 10.0%, and the remainder by both parents. Aerial prey transfers from adults to flying young
were feet-to-feet or through aerial drops. The hypothesis that parent peregrines make live-drops of prey
to their fledged young to teach them how to hunt is confounded by observations that live-drops of just-
caught prey are also made by the adult male to his mate. However, the hypothesis that peregrines assist
their young in capturing prey is supported by anecdotal evidence.

Keywords: Peregrine Falcon-, Falco peregrinus; tandem hunting, fledgling hunting, adult hunting cooperative

hunting.

CAMBIOS EN EL EXITO DE FORRAJEO Y CAZA COOPERATIVA EN UNA PAREJA DE FALCO PER-
EGRINUS Y SUS VOLANTONES

Resumen. — Se estudiaron los habitos de forrajeo de una pareja de Falco peregrinus que anido en una
planta de energfa en el centro de Alberta a lo largo de siete epocas reproductivas consecutivas (1998 a
2004). Observamos 386 ataques, los cuales resultaron en 117 capturas de presas. La tasa de exito se
incremento del 21.9% en el primer ano al 39.1% en el septimo ano, y en promedio fue del 30.3%. La
mayoria de los eventos de caza (76.7%) fueron iniciados a partir de vuelos elevados; los halcones
emplearon frecuentemente el aire caliente que se encontraba encima de las columnas de humo de la
planta para alcanzar mayores alturas. La tasa de exito de los ataques iniciados en vuelo no fue signifi-
cativamente diferente de la de los ataques iniciados desde perchas (28.7% versus 35.6%). Los eventos
de caza en los que ambos miembros de la pareja participaron en tandem {N = 100) fueron mas exitosos
que aquellos en los que participo un solo individuo (39.0% versus 27.3%), pero la diferencia no fue
significativa. Las presas predominantes fueron la gaviota Larus pipixcan y varias aves paserinas pequenas,
representando el 53.0% y el 27.4% de las capturas, respectivamente. Existio una diferencia significativa
en las tasas de captura de los distintos tipos de presa (42.5% para L. pipixcan y 24.1% para las aves

^ Email address: tj_dick_dekker@hotmail.com

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Foraging Success of Peregrine Falcons

395

paserinas) . Las tasas de exito no fueron diferentes entre el macho y la hembra, pero existio una notable
diferencia en los taxa capturados por cada individuo. El macho capture el 84.4% de las aves paserinas,
pero solo el 22.9% de las gaviotas. Despues del primer ano, existio un cambio significativo de paserinas
a gaviotas de forma paralela con un cambio significativo en la participacion de los miembros de la
pareja en el forrajeo. Todas las gaviotas capturadas por el macho fueron entregadas a la hembra o a
los volantones. En el 23.3% de los eventos de caza, uno o los dos padres estuvieron acompahados por
uno o mas volantones. El macho participo en el 76.7% de todas las cacerias en las que participaron
volantones {N = 90), la hembra en el 10.0% de estas, y ambos individuos en el porcentaje restante. Los
adultos entregaron las presas a los juveniles en vuelo directamente de garras a garras, o dejandolas caer
en el aire. La hipotesis de que los parentales dejan caer presas vivas para ensenarles como cazar a sus
volantones es dificil de apoyar ya que el macho adulto tambien dejo caer presas recien capturadas en
vuelo para que su pareja las tomara. Sin embargo, la hipotesis de que los peregrinos le ayudan a sus
volantones a capturar presas es apoyada por informacion anecdotica.

[Traduccion del equipo editorial]

Cooperative or tandem hunting by mated pairs
of Peregrine Falcons {Falco peregrinus), in which
both partners attack the same prey simultaneously,
has been reported from many locations across the
species’ worldwide range (e.g., Cade 1960, Bird
and Aubry 1982, Thiollay 1988, Frank 1994, Tre-
leaven 1998, Jenkins 2000). The success rate of tan-
dem hunts has been reported to be higher than
hunts by single peregrines (Thiollay 1988), but
whether or not tandem hunting by mated pairs ac-
tually involves a degree of coordination between
the two individuals is unclear. On their breeding
range, Peregrine Falcons are also known to hunt
together with their fledglings, although data are
limited (Brown and Amadon 1968, Palmer 1988,
White et al. 2002). The notion that juvenile pere-
grines need to be taught hunting skills by their par-
ents is contradicted by the fact that captive-reared
peregrines, deprived of parental instruction, begin
pursuing and capturing prey at about the same age
as young falcons at natural nest sites (Cade and
Burnham 2003). Apparently, the peregrine does
not need to be taught how to chase and kill prey
(Cade 1982, Sherrod 1983). However, Newton
(1979) and Ratcliffe (1993) state that more critical
observation is needed during the period in which
fledglings achieve independence.

This paper presents empirical data on the for-
aging behavior of one mated pair of peregrines
hunting solo or in tandem over seven consecutive
breeding seasons. Additionally, we present anec-
dotal observations on parent-fledgling interac-
tions.

Study Area and Methods

The study area is in central Alberta, Canada, at 53°N.
In this largely agricultural region, peregrines nested com-
monly on cliffs and cutbanks along rivers and creeks until

they became extirpated (Dekker 1967, Fyfe 1976). A gov-
ernment program of releasing captive-reared peregrines
in central Alberta began in 1975 and led to the establish-
ment of breeding pairs on city buildings by 1981 (Hol-
royd and Banasch 1990). By the mid 1990s, peregrines
began using nest boxes on high industrial structures in
rural regions. The breeding site selected for this study is
a power plant on the north shore of Wabamun Lake,
which is roughly 8 X 20 km in size. The nest box was
built by the Alberta Falconry Association in 1993 and put
in place by TransAlta Utilities (Wabamun, Alberta) on a
catwalk just below the top of a 91 m smoke stack. Lower
down, the flat roof of the main building functions as a
landing pad for newly-fledged young. Power line pylons
in the vicinity provide high perches and plucking posts.
Settling ponds and bare ground adjacent to the plant are
used as loafing areas by the fledglings and by the adults
that bring down large prey such as gulls and ducks. The
landscape around the Wabamun plant is mainly wooded
with small marshes and an extensive area (5-10 km^) of
excavated and reclaimed terrain to the north. The lake
receives light recreational use, and some shoreline sec-
tions are developed with cottages and small marinas.

The nest box is in plain view from a public road that
runs between the lake and the plant. Depending on
weather conditions, we watched from different vantage
points 0.1-2 km away, and we used 8X wide-angle bin-
oculars and 20— 60X telescopes. Observation periods, last-
ing 3-6 hr each, usually between mid-afternoon and sun-
down, were spaced arbitrarily and increased during the
period when the fledglings were on the wing. Over 7 yr,
1998—2004, the number of observation days was 196; 15
in June, 58 in July, 101 in August, 21 in September, and
1 in October. The only two days of observation in 1997
were added to the 1998 total. The median date when the
first juvenile (always a male) fledged was 16 July (13-25
July). The number of young fledged was three or four
per season with a mean of 3.6 (N = 11 males and 14
females). As indicated by their leg bands and plumage
characteristics, the breeding pair consisted of the same
individuals for the duration of the study, and we classified
the female as a 2-yr old falcon in 1998 based on her
brown dorsal color in 1997. The subspecific origin of
these falcons is F. p. anatum and both originated from
captive-reared stock nesting in the cities of Edmonton

396

Dekker and Taylor

VoL. 39, No. 4

and Calgary (Gordon Court, Alberta Environment, pers.
comm.).

Prey species upon which peregrines are known to feed,
such as waterbirds and small passerines, are common in
the study area. With a mass of 220-335 g (Dunning
1984), the Franklin’s Gull {Larus pipixcan) is close to the
mass limit that male peregrines can or are willing to carry
over long distances. Although Franklin’s Gulls are locally
scarce in early summer, large migrating flocks begin ar-
riving in mid-July. Rock Pigeons (Columba livid), which
are the dominant prey for peregrines in human altered
environments (Ratcliffe 1993), were resident at the plant
site but only in small numbers (<20).

The terms hunt and attack are used interchangeably
and represent one attempt at capturing prey including
one or more stoops or passes at the same target of which
the outcome was known. Tandem hunts were simulta-
neous attacks by both adults on a flock of prey or an
individual prey. Group hunts by a combination of parents
and juveniles were tallied as adult hunts, and their kills
were considered to have been made by the adults, al-
though in a few cases it was the juvenile which actually
seized (or was allowed to seize) the prey. Hunts by juve-
niles alone were not tallied.

Details of hunts and kills were entered into field diaries
and annotated tabulations. Observer bias in comparing
results between years, we believe, was not a factor as D.
Dekker recorded observations over the 7-yr study period.
R Taylor was associate observer the last 3 yr of the proj-
ect. Data sets were compared for significance by chi-
square Test of Independence with a Williams’ correction
as described in Sokal and Rohlf (1981).

Results

Hunting Methods and Prey Species. We ob-
served 386 hunts by the adult peregrines. Nearly
all (99.5%) were directed at airborne prey and
consisted of two primary methods: attacks

launched from soaring flight (76.7%) or from a
perch (23.3%; Table 1). The falcons typically be-
gan a soaring sequence by circling up over the
plant and using the hot air of the three stacks to
gain height rapidly. Drifting downwind, the soaring
falcons reached altitudes estimated to exceed 1000
m. By flapping their wings or gliding, they cruised
upwind. Attacks on prey flying lower than the fal-
con were made by deep stoops with wings partly or
fully flexed. Some of these attacks began with a
burst of wing flaps and ended in a stoop, which
could either be near-vertical or oblique. If the prey
evaded the initial stoop, the falcon might follow up
with one or more additional stoops or passes.

Still-hunting attacks were launched from high
perches such as the catwalk railing near the top of
the 91 m stacks. With rapid wing flaps, these fal-
cons headed for targets some distance away (>100
m) . After unsuccessful or aborted attacks, the per-
egrines commonly returned to the plant, either to

perch or to regain altitude by soaring. Some hunt-
ing sequences lasted 3-4 hr before a prey was cap-
tured. On other days, we observed falcons catch
three prey in less than 1 hr.

The success rate of all hunts {N — 386) by the
adult peregrines, either attacking prey solo or in
tandem, was 30.3% (Table 1). Perch hunts were
not significantly (G = 0.77, P = 0.379) more suc-
cessful than soar hunts (35.5% and 28.7%, respec-
tively). The success rate of the female was 37.1%,
not significantly (G = 2.37, P — 0.124) different
from that of the male (24.1%), but there was a
notable difference in the taxa of the prey taken by
the two sexes (Table 2). The male caught 84.4%
of 32 small passerines, but only 22.9% of 62 gulls.
Nearly all gulls seized by the male were released to
his mate or a fledgling <1 sec after capture. If nei-
ther the female nor any of the fledglings were
nearby, the male, upon seizing a gull, brought it
down steeply and left it on open ground or on the
roof of the plant ( A = 5) . The female carried gulls
with apparent ease over distances exceeding 1 km.

The majority (84.9%) of gull kills observed at
close range or found as prey remains (A = 73)
were juveniles. Juvenile Franklin’s Gulls were often
seized in mid air during the falcon’s first stoop. By
contrast, adult gulls typically evaded a peregrine by
rising steeply. Some evaded two or more additional
passes and were eventually left alone. Others de-
scended and plunged into water. In seven instanc-
es, the female peregrine repeatedly swooped at the
swimming gull. Three were retrieved from the wa-
ter and carried off. Some white birds, assumed to
be gulls, that evaded 20 or more diving attacks far
out over the lake may have been Common Terns
{Sterna hirundo). Two terns were carried to the
plant, but their capture had not been observed.
Ring-billed Gulls {Larus delawarensis) were some-
times forced down, but we found no evidence that
any were killed.

Rock Pigeons were seldom attacked. On two oc-
casions, the female stooped unsuccessfully at free-
flying flocks of pigeons. Both adults made oppor-
tunistic passes at pigeons that flushed from plant
ledges below them, but the only successful pigeon
hunts (A = 2) were initiated by fledglings. In at
least one of these hunts, the capture was made by
the adult female, who joined the attack.

During the sixth year of study, we gained the im-
pression that the falcons had become more suc-
cessful — in particular, at capturing gulls — than dur-
ing the preceding years. This impression was

December 2005

Foraging Success of Peregrine Falcons

397

•D

1998 1999 2000 2001 2002 2003 2004

Years

Figure 1. Hunting success per year of the same pair of
Peregrine Falcons breeding in central Alberta, 1998—
2004. The respective number of hunts/kills for the 7 yr
of study were as follows: 108/23, 47/11, 25/8, 37/12, 44/
16, 61/22, 64/25.

strengthened in year 7 and confirmed by subse-
quent data analysis. The overall success rate of the
adults increased from 21.3% in the first year of
study to 39.1% in the seventh year of study (Fig.
1 ).

Tandem Hunts. Each year from mid June on-
wards, both parents often began soaring together.
The male gained height quicker and always circled
higher than the female. Stooping alternately, they
attacked 68 prey from soaring flights (Table 1). If
no prey had been sighted for some time, the pair
separated or headed off into the distance, one fol-
lowing the other, either in soaring or flapping
flight. Tandem attacks were also launched from
high perches on the plant. In tandem attacks, both
falcons could take the lead, and the male flew
higher than the female. While the female ap-
proached the prey directly, the male typically at-
tacked from above in a near vertical stoop. A high
percentage (60-75%) of tandem hunts were lost
from view before we could either see the target or
the result. Tandem hunts of which the outcome

was known (N = 100) represented 25.9% of all
hunts, and their success rate was higher than in
286 solo hunts (39.0% versus 27.3%), but the dif-
ference was not significant (G — 2.39, P = 0.121).
The success rate of 32 tandem attacks launched
from a perch was 50.0%, compared to 33.8% for
tandem attacks from soaring position.

Tandem hunts resulted in 39 kills (Table 1). Of
these, 26 captures of prey were observed in detail:
seven were seized by the female, 19 by the male.
Prey caught by the male in tandem attacks were
surrendered at once to the female, either by feet-
to-feet transfer (N = 5) or released in the air (N
= 14). Thirteen of these aerial drops were gulls,
which resumed flight upon release. Nine were sub-
sequently seized by the female; four evaded her
passes and were let go or escaped by splashing
down into water.

Hunts by Groups of Adults and Fledglings. In

23.3% of hunts (N = 386), one or both parents
were accompanied, and often harassed, by one or
more juveniles (Table 3) . Some fledglings closely
followed the adults prior to the start of a hunt,
others approached hurriedly from a distance to
join a hunt in progress. A significant majority of
group hunts (G = 37.96, P = 0.001) were led by
the adult male, which made 71.0% of the 31 kills
(Table 3). Prey caught by the parents were trans-
ferred, usually at once, to the approaching juve-
niles, either by feet-to-feet transfers (N = 15) or
through aerial drops (N = 7) . At least three small
passerines that were dropped were still alive and
resumed flight. They were recaptured by a juvenile
or by the adult and released again. Three live-
drops were gulls. In addition, four of 11 gulls
caught in adult-juvenile hunts were seized in flight
by the juveniles “chaperoned” by adults.

After successful group hunts, one or more juve-
niles fed on the kill. If the feeding site was in an
open area away from the plant, the adult female
typically perched on a pole nearby {N = 14). At

Table 1. Hunts and kills made by a pair of Peregrine Falcons nesting on a power plant in central Alberta, 1998-
2004. The hunting success rates are presented in parentheses.

Hunts/Kills from Soaring

Hunts/Kills from Perch

Total Hunts

Adult male (24.1%)

176/44 (25.0%)

40/8 (20.0%)

216/52

Adult female (37.1%)

52/18 (34.6%)

18/8 (44.4%)

70/26

In tandem hunts (39.0%)

68/23 (33.8%)

32/16 (50.0%)

100/39

Totals (30.3%)

296/85 (28.7%)

90/32 (35.5%)

386/117

398

Dekker and Taylor

VoL. 39, No. 4

the approach of people, she vocalized and
“swooped” overhead. She also stooped at crows or
Buteo hawks, apparently to drive them away. After
the fledglings were satiated and left, the adult fe-
male sometimes fed on the remains of the kill {N
= 5).

Discussion

Hunting Success. The hunting success of adult
peregrines on breeding territory is generally high-
er than that of migrating or wintering peregrines
(Dekker 1980, Roalkvam 1985). Jenkins (2000)
compared data presented in eight publications on
breeding peregrines and found an extreme varia-
tion (9.3-84.1%) in hunting success, but much less
variation in hunting methods. The majority (58-
75%) of attacks summarized in his review were
launched from a perch. By contrast, the percent-
age of perch hunts was only 23% at Wabamun. The
“still-hunting strategy” of perch hunts reduces the
energy cost of foraging. However, high-soaring
flight is also relatively energy-efficient and widens
the radius of the attack zone (Enderson and Craig
1997). Soaring flight has been reported as a com-
mon hunting method in many regions, but not to
such a high degree as documented in this study.
The second highest use was recorded in Africa,
where breeding pairs launched 30-42% of hunts
from flight (Thiollay 1988, Jenkins 2000). The use
of factory exhaust to facilitate soaring flight by the
Wabamun peregrines was described in an earlier
publication (Dekker 1999), but this phenomenon
has to our knowledge not been reported else-
where.

It is noteworthy that the falcons in this study at-
tacked nearly all of their prey in flight, often at
great altitudes. This is in sharp contrast to migrat-
ing or wintering peregrines, which commonly use
surprise methods to attack prey on the ground or
in shallow water (Dekker 1980, 2003, Cresswell
1996). However, there is also an element of sur-
prise involved if a soaring peregrine stoops from a
great height at prey flying far below. In solo hunts,
the male frequently made long stoops that levelled
out low over woods and were aimed at flocks of
small passerines flying just beyond the trees. Sur-
prise is probably also a factor in tandem hunts in
which the male stoops from high above while the
female pursues the prey at a lower altitude.

A key factor in the hunting success of peregrines
is the vulnerability of individual prey, which is dif-
ficult to assess for the human observer. It is well-

known that predation risk for land birds increases
over water (Herbert and Herbert 1965). Converse-
ly, water birds become vulnerable over land (Hunt
et al. 1975, Dekker 1980). Mature prey on home
territory should be harder to catch for a raptor
than juvenile prey passing over unfamiliar terrain.
In central Alberta, the migrations of juvenile prey
species approximately coincide with the period
when fledgling peregrines are on the wing and
when the parental task of provisioning them is
most demanding. In this study, the peregrines were
very successful at capturing juvenile Franklin’s
Gulls. For instance, on 7 d between 17 July and 9
August 2003, when thousands of gulls were passing
through the area, the adult female, hunting solo,
captured each of seven juvenile gulls in her first
attack of the afternoon and each requiring only
one stoop. While it does not seem surprising that
bird-hunting falcons should become better at what
they do as they become older and gain in experi-
ence, data in support of that notion have, to our
knowledge, not been published before. An expla-
nation for the year-to-year increase in the success
rate of the Wabamun pair is that these falcons be-
came specialists on juvenile Franklin’s Gulls, which
differ from adults by their dusky color and absence
of black on the head. Juvenile targets were proba-
bly pre-selected before the falcons began their at-
tack. A similar pre-selection hypothesis was ad-
vanced for the high success rate (73-93%) of “Red
Baron,” an adult male peregrine hunting over
coastal marshes in New Jersey (Cade and Burnham
2003:333).

In this study, the prey component changed sig-
nificantly after the first year (Tables 4 and 5). In
the first year of study, gulls made up only 8.7% of
kills compared to 63.8% in years 2-7 (G = 10.85,
P = 0.001). The proportion of small passerines
changed significantly from 60.9% in the first year
to 19.1% in years 2-7 (G = 7.01, P — 0.008). Over-
all, the capture success on gulls (of both age
groups) was significantly higher (G = 5.35, P =
0.021) than on small passerines (42.5% versus
24.1%). Successful taking of juvenile gulls may be
even higher than for adults, but an adequate sam-
ple was not available for adults. As reported in re-
sults, the sample of gull kills {N = 73) included
84.9% juveniles.

Coincident with the observed prey switch, we re-
corded a major change in foraging participation
between the sexes after the first year (Table 6).
The male’s solo hunts in the first year were 78.7%

December 2005

Foraging Sugcess of Peregrine Falgons

399

Table 2. Prey taxa captured by the Peregrine Falcon pair hunting solo or in tandem.

Franklin’s

Gulls

Small

Passerines

Smalt.

Shorebirds

Ducks

Other or
Unidentified

Adult male

Adult female

Pair in tandem

Totals

of total hunts (N = 108), significantly greater (G
= 8.08, P = 0.004) than the 47.1% of hunts in
years 2-7 {N = 278). By contrast, the female’s
share during the first year was 2-7%, and this rose
significantly to 24.1% in years 2-7 (G = 23.51, P =
0.001). A possible explanation is that the female
lacked skill and experience in her first year on ter-
ritory. As she became older and gained expertise,
she began to play a more active role in foraging.
There was no significant change (G = 2.70, P =
0.1) in the proportion of tandem hunts between
the first year and years 2-7 (Table 6) .

Our findings that the primary prey of the male
was passerines, whereas the female’s main prey was
gulls (Table 2), lends support to the hypothesis
that the reversed sexual size dimorphism in raptors
such as seen in the peregrine allows them to ex-
ploit a wider prey base and reduces competition
between the sexes (Selander 1966).

Cooperative Hunting. Are peregrines that attack
the same prey simultaneously with their mates or
fledglings actually cooperating? Or, are the individ-
uals simply reacting at the same time to the stim-
ulus of sighting prey? True cooperative hunting
differs fundamentally from other forms of group
predation, such as pseudo-cooperative hunting (El-
lis et al. 1993). In true cooperative hunting, the
group consists of at least two members that are a
stable social unit, and their cooperation should
benefit the group rather than just the individual.
An example of true cooperative foraging is de-
scribed by Bednarz (1988) for the Harris’s Hawk

{Parabuteo unicinctus). Ellis et al. (1993) conclude
that cooperative hunting is the most efficient strat-
egy for capturing prey in many situations and that
each form of social foraging should have evolved
as an adaptive advantage enhancing the fitness of
all individuals in the group. In the Aplomado Fal-
con (Falco femoralis), pair hunting is more than
twice as productive as solo hunting when the prey
are birds (Hector 1986). Similarly, the success rate
of pair hunting in peregrines may depend on the
species of prey hunted (Jenkins 2000).

In this study, tandem hunts by the mated pair of
peregrines were more successful than solo hunts
(39.0 versus 27.3%), although the difference was
not statistically significant. Moreover, the individu-
al success rate of the two partners in tandem hunts
is actually halved. So what, if any, is the fitness value
of tandem hunting for this pair of breeding pere-
grines? It may lie in the fact that any action by the
male that benefits his mate or their progeny
should be of adaptive advantage.

At Wabamun, the adult male was not seen to eat
the gulls he killed, although on two occasions he
fed on gull remains abandoned by fledglings. The
fact that he mainly hunted such prey in the com-
pany of his mate or fledglings suggests that his role
was a cooperative one. This view is supported by
anecdotes such as the following. By mid September
1999, after the fledglings had dispersed, the adults
were still hunting together. One evening, shortly
after both had soared up over the plant, the male
caught a small passerine and landed on a pylon to

Table 3. Hunts/kills made by one or both Peregrine Falcon parents accompanied by one or more fledglingjuveniles.

1 Juvenile

2 Juveniles

3 Juveniles

Totals

Adult Male

29/10

34/10

6/2

69/22

Adult female

3/2

6/4

0/0

9/6

Both adults

6/3

5/0

1/0

12/3

Totals

38/15

45/14

7/2

90/31

400

Dekker and Taylor

VoL. 39, No. 4

Table 4. Prey captured by a pair of Peregrine Falcons as a percentage of total prey per year.

Year

Percent Gulls

Percent Passerines

Percent Other

No. Total Prey

No. Hunts

8.7

60.9

30.4

108

63.6

27.3

9.1

62.5

12.5

25.0

58.3

16.7

25.0

43.7

31.3

25.0

63.6

27.3

9.1

80.0

4.0

16.0

Totals

53.0

27.4

19.6

117

386

consume his prey. Instead of interfering, the fe-
male perched on the next pylon and waited for her
mate to finish his meal. Presently, both soared up
again and eventually flew out high over the lake,
stooping in tandem at gulls. Like many similar ob-
servations, this incident suggests that the male’s
role was truly a cooperative one — to assist his mate
in her foraging.

The question of whether attacks on the same
prey by a combination of adults and fledglings can
be considered cooperative seems even less clear,
for it is apparent that the juvenile is primarily in-
tent on kleptoparasitizing the adult. If there is co-
operation, it is one-sided and benefits only the ju-
veniles (i.e., this may be considered as parental
investment). Nevertheless, the evolutionary value
of adult/ fledgling combinations is undeniable, as
a well-fed progeny enhances the future of the fam-
ily genes. In support of the hypothesis that the par-
ticipation of adults in joined hunts with their fledg-
lings indeed represents parental care, we present
a number of anecdotal observations in the appen-
dix.

Live-drops of Prey. Cade (1982) and Sherrod
(1983) characterize the behavior of paired male
peregrines in social interactions with their bigger
mate as submissive and even fearful. Females take
food from males in an aggressive manner, not only

Table 5. Comparison of main prey taxa captured by a
pair of Peregrine Falcons in study years 1 and 2-7.

Prey Taxa

No.

Kills

Percent of
Totals Kills

Year 1

Gulls

8.7

Years 2-7

63.8

Year 1

Passerines

60.9

Years 2-7

19.1

during the breeding season but also on migration
or at the wintering grounds. Unmated females rou-
tinely force males to drop just-caught prey (Dekker
1980, 2003). Tandem hunting by unmated pere-
grines is relatively common and driven by compe-
tition rather than cooperation. Two or more (up
to six) migrating or wintering peregrines were seen
in joint pursuit of the same prey in Alberta and
British Columbia. Male peregrines were forced to
make live-drops of prey not only to female conspe-
cifics, but also to other kleptoparasitic raptors,
such as Prairie Falcons {Falco mexicanus) and Bald
Eagles {Haliaeetus leucocephalus; Dekker 1995,
1998).

I concur with Sherrod (1983) that the release of
just-caught prey by the male peregrine at the ap-
proach of an aggressive female may be triggered
by the impulse to avoid close contact. The impor-
tance of a timely release was demonstrated on 21
August 2003, when the Wabamun male, carrying a
just-caught prey and flying 20-25 m high, was met
by a screaming juvenile female in typical begging
flight. Apparently, the male was just too late in re-
leasing his prey, for he was seized by the juvenile.
Locked by their feet, both birds tumbled about 15

Table 6. Number of hunts by the adult male and fe-
male, either hunting solo or in tandem, in year 1 and
years 2-7.

No.

Hunts

Percent
OF Total

Year 1

Adult male

78.7

N = 108 hunts

Adult female

2.7

Tandem

18.5

Years 2-7

Adult male

131

47.1

N = 278 hunts

Adult female

24.1

Tandem

28.8

December 2005

Foraging Success of Peregrine Falcons

401

m before separating again, while the prey item fell
into the bushes below and was lost.

Based on a thorough review of the literature and
on his own studies, Sherrod (1983) observed that
the behaviors of parents and fledglings comple-
ment each other. While the youngster only wants
food, the adult appears to be very willing to supply
that food. Some live-drops are no doubt the result
of the aggressive approach of the begging falcon.
However, as argued by Newton (1979), other live-
drops are clearly intentional as parent peregrines
will recapture the live-dropped prey and release it
again if the fledgling fails to catch it the first time.
Such repeat drops were seen in this and other stud-
ies (Frank 1994, Treleaven 1998).

Conclusion

Some of the aerial drops of just-caught and still
live prey from adult to fledgling (described in the
appendix) lend support to the hypothesis that the
parents were teaching their young by example. Al-
though young falcons do not need to be taught to
hunt, such extended parental care might well give
them a certain survival advantage after leaving the
nest site. The observation that live-drops were also
made from adult to adult, both at Wabamun and
at a natural nest site in northern Alberta (Dekker
1999), may seem to refute the above hypothesis.
Because there can be no doubt that adult females
are accomplished hunters, the male’s reason for
making live-drops to his mate can have nothing to
do with teaching. However, here a secondary and
complementary factor comes into play. Whether
hunting with his mate or a fledgling, the male plays
a dual role, either in support of his mate or prog-
eny.

It is difficult, if not impossible, to translate all of
the anecdotes detailed in the appendix into hard
data in support of the teaching hypothesis. As to
the alternative, but not exclusive, hypothesis that
parent peregrines assist their fledglings in captur-
ing their first prey, on the evidence presented
here, we are convinced that the answer is affirma-
tive.

ACKNOWI.EDGMENTS

I thank T.J. Cade for his review of an earlier draft of
this paper. Referees G. Malar and I. Newton made very
helpful comments on the second version. Throughout,
the input ofj. Bednarz was particularly valuable. W. Nel-
son provided relevant information on nest box installa-
tion and the weight of Franklin’s Gulls. G. Court did the
statistical tests. R. Dekker drafted the figure. Occasional

co-observers were G. Court, I. Dekker, K. Kunst, and J
Morrison. I thank TransAlta Utilities for access to obser-
vation points out of bounds to the general public. All
expenses incurred during this study were privately fund-
ed by the authors except during the last year, when D
Dekker received travel grants from TransAlta Utilities
and the Alberta Conservation Association.

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Received 18 September 2003; accepted 15 July 2005

Appendix. Observations of parental care by a pair of per-
egrines toward their fledglings and nearly-fledged juve-
niles.

(1) On 16 August 1999, having stooped at a gull and
missed his target, the adult male maneuvered under it in
a peculiarly slow flying style. He appeared to drive the
gull upward and prevent it from dropping into the water

below. Seconds later, a juvenile female stooped from
above, just missing the gull. The adult male then stooped
again, just short of the target. Chased by both peregrines,
the gull eventually escaped. In this case, as in others, it
seemed clear that the male did not want to catch the gull
himself. Instead, he attempted to set it up for the ap-
proaching juvenile.

(2) On two occasions, when a gull was chased by a
group of one adult and one fledgling, the adult hit or
touched the prey, causing it to cartwheel in the air. In
the next instant, the gull was seized by the closely-follow-
ing juvenile. Our impression was that the adults were not
intent on taking the gull themselves.

(3) On 12 August 2000, the adult male, while soaring
in tandem with his mate, suddenly sprinted away (400—
500 m) to hit a shorebird that was being chased by two
juveniles at an altitude estimated at 75 m. Dead or
stunned, the prey fell into reeds and was lost before the
juveniles could recover it. This was one of only four in-
stances when these peregrines hit their prey in the air,
as opposed to the common method of binding to the
prey and carrying it down. The remarkable point is that
the adult male did not stoop and recover the plunging
shorebird himself, which would have been a normal pro-
cedure if he had been hunting alone.

(4) A Rock Pigeon pursued by a fledgling was taken
by the adult female, who transferred it at once to the
juvenile. On their own, the adults seldom pursued pi-
geons.

(5) Fledglings that have been on the wing for only a
few days have difficulty carrying a gull. After making an
aerial transfer to an unskilled juvenile, the adults will ac-
company it in flight and retrieve the gull if dropped. By
the same token, seemingly aware of the lack of ability in
a badgering female youngster, the adult female refused
to transfer a just-caught gull and instead carried it ca.
500 m to the roof of the plant, where she at once sur-
rendered it to the fledgling.

(6) The adult male demonstrated an awareness of the
different needs of the genders. In group hunts with male
offspring, he selected mostly passerines or small shore-
birds (41 of 45). By contrast, he usually attacked gulls in
the company of females. After capturing one or more
gulls for his mate or the fledglings, he hunted smaller
prey for himself.

The above interactions between parents and fledglings
parallel numerous anecdotes described by long-term per-
egrine observers in New York and Great Britain (Frank
1994, Treleaven 1998).

It is our impression that adult peregrines appear to
know how to assist their progeny in gaining indepen-
dence. For a start, there is a change in food exchanges
when the first of the juveniles are close to fledging. Both
at Wabamun and a natural nest site in central Alberta,
the adult male appeared to coax a fully-feathered male
youngster to fly. Instead of transferring the prey item in
the usual direct manner, he cruised back and forth just

December 2005

Foraging Success of Peregrine Falcons

403

out of reach, holding the prey in his lowered feet. His
behavior cannot be explained as having been prompted
by fear of a bigger bird for this incident involved a male
juvenile. After the young male failed to fledge, the adult
gave the food item to another juvenile, a fully-feathered
female sitting on the catwalk. Similarly, on two other oc-
casions when he arrived with a small prey, he flew right
up to a screaming juvenile male that was perched on the
edge of a catwalk, but instead of exchanging the prey
feet-to-feet, he dropped it and recovered the falling item
in a quick stoop. He repeated this teasing show three or
four times. After the fully-feathered juvenile male failed

to fly, the adult gave the food item directly to a less-de-
veloped female still in the nest box.

Another noteworthy exchange involved the female
One day, after she had delivered a prey to two juvenile
males, which shared the food, the male arrived, also with
prey. He gave it directly to one of the same two young-
sters. Instantly, the adult female interfered. She took the
food item away from the young male and offered it in-
stead to a juvenile female which had not been fed for
several hours. Similar incidents were seen at Wabamun
and at a natural nest site in central Alberta (D. Dekker
unpubl. data).

J Raptor Res. 39(4):404-416
© 2005 The Raptor Research Foundation, Inc.

NESTING ECOLOGY AND BEHAVIOR OF BROAD-WINGED HAWKS
IN MOIST KARST FORESTS OF PUERTO RICO

Derek W. Hengstenberg and Francisco J. VilellaI

USGS Biological Resources Division, Cooperative Research Units, MS 9691, Department of Wildlife and Fisheries,

Mississippi State University, Mississippi State, MS 39762 US. A.

Abstract. The Puerto Rican Broad-winged Hawk {Buteo platypterus brunnescens) is an endemic and

endangered subspecies inhabiting upland montane forests of Puerto Rico. The reproductive ecology,
behavior, and nesting habitat of the Broad-winged Hawk were studied in Rio Ab^o Forest, Puerto Rico,
from 2001-02. We observed 158 courtship displays by Broad-winged Hawks. Also, we recorded 25 ter-
ritorial interactions between resident Broad-winged Hawks and intruding Red-tailed Hawks {Buteo ja-
maicensis jamaicensis) . Broad-winged Hawks displaced intruding Red-tailed Hawks from occupied terri-
tories (P = 0.009). Mayfield nest survival was 0.67 across breeding seasons (0.81 in 2001, N = 6; 0.51
in 2002, N = 4), and pairs averaged 1.1 young per nest (years combined). The birds nested in mixed
species timber plantations and mature secondary forest. Nests were placed in the upper reaches of large
trees emerging from the canopy. Nest tree DBH, understory stem density, and distance to karst cliff wall
correctly classified (77.8%) nest sites.

Key Words: Broad-wing Hawk; Buteo platypterus brunnescens; endangered; nest success; prey delivery; hab-

itat model; karst forest; Puerto Rico.

ECOLOGIA REPRODUCTIVA DE BUTEO PiJiTYPTERUS BRUNNESCENS EN BOSQUES DE CALIZA
HUMEDOS DE PUERTO RICO

Resumen. Buteo platypterus brunnescens es una subespecie de rapaz endemica a los bosques montanos

de Puerto Rico. Investigamos la ecologia reproductiva y el comportamiento de B. p. brunnescens en el
Bosque de Rio Abajo, Puerto Rico, durante 2001 y 2002. Observamos 158 despliegues de cortejo en
Rio Abajo. Observamos 25 encuentros territoriales entre B. p. brunnescens y B. jamaicensis jamaicensis. B.
p. brunnescens desplazo a B. j. jamaicensis de sus territorios el 84% de las veces (P = 0.009). La supervi-
vencia de los nidos en ambas temporadas fue de 0.67 (0.81 en 2001, N = 6; 0.51 en 2002, N= 4). Los
nidos produjeron un promedio de 1.1 volantones por nido (afios combinados). Encontramos nidos en
areas de bosque secundario maduro y plantaciones forestales. La altura del dosel, diametro del arbol,
densidad del sotobosque y distancia a farallon de mogote clasificaron correctamente (77.8%) los nidos
en Rio Abajo.

[Traduccion de los autores]

The Broad-winged Hawk {Buteo platypterus brun-
nescens) is an endemic woodland raptor of upland
montane forests of Puerto Rico. This subspecies is
listed as endangered (Federal Register 1994) hy
the Puerto Rico Department of Natural and Envi-
ronmental Resources (DNER) and the U.S. Fish
and Wildlife Service (USFWS). The Broad-winged
Hawk in Puerto Rico is nonmigratory and exhibits
a limited geographic range with known popula-
tions restricted to montane forests (Delannoy
1997). Breeding in Puerto Rico begins in late De-
cember, with nests placed in the upper reaches, but

^ Corresponding author email address; Mlella@cfr.
msstate.edu

below the high canopy (Delannoy and Tossas
2002). This insular subspecies is smaller and dark-
er than its North American nominate counterpart
Buteo platypterus platypterus, but larger than the
Lesser Antillean subspecies (Raffaele 1989, Good-
rich et al. 1996). The most recent population es-
timate for the Broad-winged Hawk in forest re-
serves of Puerto Rico is approximately 125
individuals (Delannoy 1997).

The nesting biology of the Broad-winged Hawk
in North America has been described by a number
of authors (e.g., Fitch 1974, Matray 1974, Rosen-
held 1984, Titus and Mosher 1987, Crocoll and
Parker 1989). However, knowledge on the repro-
ductive biology of the insular endemic subspecies

404

December 2005

Puerto Rican Broad-winged Hawk Ecology

405

BWHA nest sites

A 2001

• 2002

Forest trails

Roads

Rivers

Lago Dos Bocas
Rio Abajo Forest

900 0 900 Meters

Figure 1. Locations of Broad-winged Hawk nest sites during the breeding season of 2001 and 2002 in Rio Abajo
Forest, Puerto Rico.

of Puerto Rico, and forest raptors of the West In-
dies in general, are limited (Goodrich et al. 1996).
Similarly, the available information on nesting be-
havior and diet of Broad-winged Hawks in Puerto
Rico is based on a few observations by Snyder and
Kepler (1987).

Additional information on the Puerto Rican
Broad-winged Hawk’s reproductive ecology and
nest habitat use is required to better understand
current limiting factors, and provide recommen-
dations for future research on habitat conservation
in public and private lands. Herein, we report on
the nesting ecology and behavior of the Broad-
winged Hawk in a forest reserve in the moist lime-
stone forest region of Puerto Rico. Specifically, we
provide baseline information on courtship behav-
ior and territorial defense, nest success and pro-
ductivity, prey delivery rates by nesting pairs, and
their habitat use. Moreover, we discuss the impli-
cations our results on interactions between the
Broad-winged Hawk and Red-tailed Hawk {Buteoja-

maicensis jamaicensis) may have on future plans to
establish a second wild population (by releasing
captive-reared individuals) of the critically endan-
gered Puerto Rican Parrot {Amazona vittata) in the
Rio Abajo Forest (White et al. 2005).

Study Area and Methods

Study Area. We studied Broad-winged Hawks in the Rio
Abajo Forest and surrounding private lands in Puerto
Rico from 2000-02 (Fig. 1). The Rio Abajo Forest
(18°20'N, 66°42'W) is managed by the Forestry Division
of DNER and is in west-central Puerto Rico within the
moist limestone region of the island (Ewel and Whitmore
1973). This forest reserve comprises an area of 2300 ha
with elevations ranging from 200-420 m. We obtained
climate data for the study period from the site closest to
our study area, the Dos Bocas NOAA weather station
(NOAA 2002).

Annual precipitation during our study averaged 18.3
cm (range = 6.9-34.9 cm) in 2001 and 14.7 cm (range
= 5.2-45.1 cm) in 2002. Mean annual temperature was
25.3°C (range = 19.9— 30.6°C) in 2001 and 25.5°C (range
= 20.1-30.9°C) in 2002.

The rugged limestone region (i.e., karst) of Puerto

406

Hengstenberg and Vilella

VoL. 39, No. 4

Rico encompasses 27.5% of the island’s surface (Lugo et
al. 2001). Topography in this region is extreme and char-
acterized by karst formations of subterranean drainages,
caves, dome shaped hills or “mogotes,” and deep sink-
holes. Karst forest contains the largest tree species rich-
ness of Puerto Rico (Lugo et al. 2001). Rio Abajo Forest
IS fragmented on the eastern end by a double lane high-
way and in the south-central part by a small community
(Fig. 1) . About 75% of the forest is within the subtropical
wet zone, the remaining quarter lies within the subtrop-
ical moist zone (Ewel and Whitmore 1973).

Previous studies indicated Broad-winged Hawks in
Puerto Rico have a limited geographic range, and their
abundance is higher in the Karst region compared to
other life zones on the island (Delannoy 1997). As our
primary objectives were to expand current knowledge on
breeding ecology, habitat use, and movement patterns of
Broad-winged Hawks (Hengstenberg and Vilella 2004),
we selected the Rio Abajo Forest. Moreover, we were in-
terested in comparing our results with findings of re-
cently completed studies in Rio Abajo Forest (Delannoy
and Tossas 2002).

Vegetation of Rio Abajo is comprised of a mix of sec-
ondary growth forests and timber plantations (Cardona
et al. 1987). The midstory of some areas of secondary
forest was characterized by abandoned shade-grown cof-
fee and citrus plantations. Forest overstories were domi-
nated by moca {Andira inermis) , capa prieto ( Cordia allio-
dora), and guaraguao {Guarea guidonia). Approximately
6.9% of the forest (171.7 ha) are managed timber plan-
tations. Some stands are actively maintained (open un-
derstory), while others had a developing understory.
Timber plantations, approximately 30-50 yr old, of Hon-
duras mahogany {Swietenia macrophylla) , maria {Calophy-
llum brasiliense) , teca (Tectona grandis), and mahoe {Hibis-
cus elatus) occur in valley bottoms and along mid-slopes
(Cardona et al. 1987).

As part of additional research efforts, we trapped
Broad-winged Hawks in Rio Abajo Forest (Hengstenberg
and Vilella 2004). Between January 2001 and July 2002,
we trapped eight Broad-winged Hawks in the Rio Abajo
Forest. We used octagonal and quonset style bal-chatri
traps (Berger and Mueller 1959, Erickson and Hoppe
1979), a modified dho-gaza trap (Hamerstrom 1963,
Clark 1981) with a live Red-tailed Hawk, and a Rock Pi-
geon {Columba livia) with noose harness.

Each captured individual was banded with a unique
color-coded leg band on the left leg and a standard U.S.
Geological Survey (USGS) Bird Banding Laboratory
band on the right leg. We also recorded morphometric
measurements and determined gender. We collected a
small amount (±5 mL) of blood from the brachia vein
of the left wing of every captured individual and deter-
mined gender through DNA typing. Each bird was fitted
with a backpack mounted radio transmitter attached via
a break-away backpack harness and a leather keel patch
(Vekasy et al. 1996), Furthermore, we used visible size
differences and markings to separate individual members
of a broad-wing pair.

Territorial Defense. We documented territorial en-
counters between resident Broad-winged Hawks at Rio
Abajo Forest and surrounding lands. Moreover, to ex-
amine the behavioral interactions of the two sympatric

Buteos, we observed territorial interactions between
Broad-winged Hawks and intruding Red-tailed Hawks
from limestone hilltops. We recorded the behavior of
both birds (aggressive or passive) and the end result (de-
terred or not deterred) . We used a binomial sign test for
a single sample (Daniel 1990, Sheskin 2000) to test the
hypothesis that both species of raptors displaced the oth-
er randomly during aerial displays.

Nest Searches and Monitoring. Broad-winged Hawk
use areas were delineated through direct observations
from limestone hills and hawk locations were plotted on
USGS topographic quadrangles. We then extensively
searched areas with radio-marked adults and document-
ed aerial displays or other territorial behavior. Spot maps
and historical nesting information were used to extend
our searches into other potential nesting territories. All
potential nests were monitored for reproductive activity
beginning in February of each year.

When a nest site was located, we built observation
blinds 50—100 m from the nest tree at a location on a
nearby cliff wall looking down on the nest with clear line-
of-sight visibility. In one instance, it was not possible to
build a blind with a direct view because of nest location,
dense vegetation, or steep rock walls. In this instance, the
nest was monitored from the ground at a similar dis-
tance. Nest activities were recorded throughout the
breeding season using spotting scopes, video cameras,
and binoculars from the observation blind. The distance
(m) between all occupied nests (nest-site spacing) for the
2001 and 2002 breeding seasons was measured on the
ground with surveying tape and verified on a study area
map with Geographical Information System (GIS) mea-
surements. A two-sample ^-test was used to determine if
the spatial distribution of nest sites varied between years
(Sheskin 2000).

Continuous nest observations were conducted daily
throughout the breeding season. Nest checks were ran-
domly conducted throughout the day to include all hours
when Broad-winged Hawks were active. Based on nest ob-
servations and nest checks, we estimated dates of incu-
bation, hatching, and fledging. We calculated nest sur-
vival (Mayfield 1975) from start of incubation to fledging
(total nest survival) and determined nest attentiveness
patterns. A nest was considered successful if the pair pro-
duced young. We estimated Mayfield nest survival during
the incubation and nestling periods using a combined
total of 198 incubation exposure-days and 274 nestling
exposure-days.

Prey Delivery. Food provisioning by adult Broad-
winged Hawks to the nest during the breeding season was
determined from direct observation. To assess if the birds
regularly delivered prey throughout the day, occupied
nests were monitored weekly in equal proportion during
four time periods: early morning (0800-1100 H), early
morning to mid afternoon (1101-1400 H), mid after-
noon (1401—1700 H), and late afternoon to early evening
(1701-2000 H). Nests were monitored from hatching un-
til the young fledged or the nest failed. We calculated
the mean number of prey items delivered and the pro-
portion of prey deliveries per time period. We divided
the prey items into two general categories, large (e.g.,
birds and rats) and small (e.g., macroinvertebrates and
lizards) , to determine prey provisioning patterns.

December 2005

Puerto Rican Broad-winged Hawk Ecology

407

An analysis of variance in a randomized complete
block design (PROC GLM; SAS Institute 1999) was used
to test if Broad-winged Hawks delivered total number of
prey items (response variable) per time period (block),
number of large prey items per time period, and number
of small prey items per time period equally throughout
the day. We used multiple comparisons (Least Scientific
Difference Means) of mean number of prey items
(pooled, large, and small) to examine significant values
(a = 0.05) and determine which time periods differed
with respect to number of prey items delivered (Sheskin
2000 ).

Nest Habitat Model. Areas used by broadwings for
nesting at Rio Abajo are valleys with tall forest bounded
by limestone ridges and cliff walls, where pairs soar along
their respective ridge tops (Delannoy and Tossas 2002).
Forest vegetation along cliff walls and limestone ridges
are used by resident broadwings for perching, but not
for nesting (Hengstenberg and Vilella 2004). Our pri-
mary objective was to assess which stand-level variables
best described a broadwing nest within the context of the
surrounding habitat at Rio Abajo Forest. Therefore, veg-
etation characteristics and structure around nest sites
were measured at the end of the breeding season and
following post-fledging dependency.

One nest used both in 2001 and 2002, was included
once in the analyses. We described a nest site as all veg-
etation within a 0.04 ha plot (11.3-m radius) centered on
the nest tree (Titus and Mosher 1981). We recorded hab-
itat measurements on nine of ten occupied nests and
nine nonuse sites using standard procedures (James
1971). We used a random numbers table to determine a
distance and azimuth to travel from a particular nest site
to an equivalent nonuse site. We constrained selection of
random sites to forested area within a 400-m radius of
the nest tree. All random sites were within the nest tree
stand in valleys and side slopes. The closest tree to the
plot center was chosen as the center point, and habitat
variables were measured accordingly.

We recorded visual obscurity of the understory using a
2 m Nudds board (Nudds 1977). The board consisted of
four 0.5 m sections with 30 orange and white squares.
Nudds board measurements were taken from each car-
dinal direction at a distance of 10 m from center point.
Percentage visual obscurity for the four cardinal direc-
tions was averaged for each 0.5 m section. We recorded
altitude, aspect, percentage slope, and distance to the
nearest rock wall, water, and man-made opening. All
woody plants over 2 m tall according to species, diameter
at breast height (DBH) , height, and vertical stratification
were recorded. Vertical structure was classified into three
strata heights (1-understory, 2-midstory, 3-overstory).
Nest heights were recorded directly with a measuring
tape. Tree heights were measured either by clinometer
or through visual estimation. We tested for differences in
height between clinometer readings and visual estima-
tions using a two-sample West (SAS Institute 1999). We
used a spherical densitometer to collect four readings of
canopy cover from each cardinal direction at a distance
of 5 m from center point. We calculated a mean to esti-
mate percentage overstory canopy cover.

Because of the paucity of information on nest site char-
acteristics of Broad-winged Hawks in Puerto Rico (U.S.

Fish and Wildlife Service 1997), we decided to record as
much information as possible. We measured all variables
considered biologically relevant to woodland raptors (Ti-
tus and Mosher 1981). We tested habitat variables for
normality using a Kolmogorov-Smirnov Goodness-of-Fit
Test (Sheskin 2000). As data were normally distributed,
we then used two-sample t-tests to identify variables that
differed between nest sites and random sites. Uncorre-
lated significant variables were selected for the variable
selection model (see Table 1 for variables considered).
Logistic regression analysis and AIC modeling was used
to determine which variables best discriminate a Broad-
winged Hawk nest site from a random site (PROC LO-
GISTIC; SAS Institute 1999).

To develop broadwing-habitat nest site relationships,
we utilized a two model approach (variable selection and
model selection) . For both microhabitat analyses, an in-
formation-theoretic approach was used for model selec-
tion and inference (Burnham and Anderson 2002). We
used Akaike’s information criterion (AIC,.), delta AIC
(A,), and Akaike’s ranking weight (w,) to determine the
best model.

Because of the small number of nest sites {N = 9), we
recognized the variable selection model may produce bi-
ased results (Milliken and Johnson 1984). Therefore, we
conducted an alternative AIC model selection approach
to assess which biologically-relevant variables best de-
scribed Broad-winged Hawk nest sites. This alternative
analysis models the particular nest sites without use of
stand-level comparisons (nest site versus random site) as
in the variable selection model.

For the alternative model selection, we chose 10 ex-
planatory variables from a list of 27 microhabitat vari-
ables (Table 1) based upon literature review and person-
al field experience (Titus and Mosher 1981, Delannoy
and Tossas 2002). Variables chosen were: aspect, slope,
road, rock wall, DBH, canopy cover, Nudds 2, midstory
number of stems, overstory number of stems, and canopy
height (Table 2). Nest or center tree height was excluded
because it is significantly correlated with DBH. Best mod-
el selection was based on criteria stated by Burnham and
Anderson (2002).

Results

Breeding Behavior and Territorial Defense.

From January to March of 2001 and 2002, we ob-
served 158 courtship display flights by known pairs.
Most (68%) aerial displays occurred 0917-1107 H
{x = 1012 H). Across two breeding seasons, we doc-
umented courtship display behavior in 26 pairs
throughout the Rio Abajo Forest and surrounding
private lands. Of the eleven pairs identified in
2001, occupied nests were located for six of these.
In 2002, courtship behavior was observed by 8 of
the 11 pairs recorded in 2001.

We observed 25 territorial interactions between
Broad-winged Hawks and intruding Red-tailed
Hawks. Broad-winged Hawks displaced Red-tailed
Hawks 84% of the time when an intruding Red-

408

Hengstenberg and Vilella

VoL. 39, No. 4

Table 1. Nest habitat characteristics (mean ± SD, range) measured within 0.04 ha of Broad-winged Hawk nest and
random sites in Rio Abajo Forest, Puerto Rico, 2001 and 2002.

Habitat Characteristics

Nest Site (9)

Random Site (9)

Mean ± SD

Range

Mean ± SD

Range

Altitude (m)

235.7 ± 58.0

(150-330)

219.9 ± 62.7

(126-320)

Aspect

204.9 ± 105.1

(32-340)

192.7 ± 108.8

(12-334)

Slope (%)

46.0 ± 19.0

(18-88)

30.1 ± 24.3

(0-85)

Distance to water (m)

194.1 ± 127.1

(37-450)

174.1 ± 120.7

(3-370)

Distance to road or trail (m)

68.6 ± 35.5

(25.8-135.0)

40.8 ± 42.8

(3.5-133.0)

Distance to cliff wall (m) *

41.1 ± 19.0

(13-75)

71.8 ± 30.2

(35-137)

Nest or center tree height (m)*

22.2 ± 7.7

(16.0-35.1)

12.8 ± 5.2

(6.5-22.0)

Nest or center tree DBH (cm)*

46.1 ± 15.6

(23.0-74.5)

25.2 ± 13.5

(6.9-42.5)

Nest height (m)

16.3 ± 5.6

(10.0-25.9)

—

Percentage nest height

73.5 ± 6.7

(58.8-81.3)

—

Canopy cover (%)

85.2 ± 5.8

(72-91)

81.3 ± 6.0

(70-88)

Nudds 0.5 m (%)

90.1 ± 11.5

(63.7-100.0)

75.9 ± 17.6

(53.8-97.5)

Nudds 1.0 m (%)

75.8 ± 14.2

(59.6-97.5)

59.5 ± 25.4

(21.6-87.6)

Nudds 1.5 m (%)*

74.4 ± 14.8

(51.3-95.9)

55.7 ± 18.0

(25.8-77.7)

Nudds 2.0 m (%)*

77.1 ± 9.9

(63.7-92.6)

52.9 ± 24.5

(15.9-83.5)

Midstory species richness

11.1 ± 5.6

(3-18)

12.0 ± 4.8

(7-21)

Midstory # of stems

35.8 ± 16.7

(10-58)

58.6 ± 34.2

(18-124)

Midstory stem DBH 1-4.9 cm

15.9 ± 12.7

(1-36)

27.4 ± 21.7

(0-65)

Midstory stem DBH 5-8.9 cm

9.0 ± 6.1

(2-19)

16.0 ± 14.1

(2-50)

Midstory stem DBH s 9

10.9 ± 5.3

(7-22)

16.3 ± 8.3

(4-33)

Overstory species richness

3.1 ± 2.0

(1-6)

3.4 ± 1.9

(2-7)

Overstory # of stems

10.2 ± 5.0

(3-17)

7.9 ± 5.1

(2-16)

Overstory stem DBH ^ 25.9 cm

3.3 ± 2.9

(0-9)

3.0 ± 3.9

(0-10)

Overstory stem DBH 26-49.9 cm

5.6 ± 3.2

(2-11)

4.2 ± 3.5

(0-12)

Overstory stem DBH ^ 50 cm

1.3 ± 1.4

(0-5)

0.7 ± 0.9

(0-2)

Basal area m^/ha

31.8 ± 13.6

(14.2-53.4)

28.2 ± 14.0

(9.0-56.7)

Canopy height (m)

17.9 ± 2.8

(14.4-23.4)

16.6 ± 4.3

(13-26)

* Significant Kest (P < 0.05).

tailed Hawk entered an occupied territory (p^ =
21/25 = 0.84, P = 0.009, 2-tailed test). In every
aerial encounter, the Red-tailed Hawk was the in-
truding species. All aerial encounters involved
adult birds of both species. Aerial displays involv-
ing one Broad-winged Hawk and one Red-tailed
Hawk occurred 72% of the time. However, Broad-
winged Hawk pairs flew in unison 28% of the time
to defend their territory against Red-tailed Hawks.

Displays varied from “high-intensity flights” with
intruders to “low-intensity flights” between pairs.
During displays both birds circled together in close
proximity and in the same general direction with
the male broadwing flying above the female. Dur-
ing low-intensity flights, adults soared upward on
widespread wings and fanned tails. In high-inten-
sity displays, the adults would alternate between
wing flaps and soaring. When the male reached
the top of the flight, he performed undulating

dives or dipping flight (Wiley and Wiley 1981,
Brown and Amadon 1989), consisting of a series of
2-7 shallow dives made toward the female. Most
other displays ended with the birds diving straight
back with cupped wings at high speeds into the
canopy, known as parachuting (Wiley and Wiley
1981, Goodrich et al. 1996).

Altitude gained varied among displays; generally
the longer the flight, the higher the altitude ob-
tained. Flights ranged from about 50 m above the
tree canopy to elevations over 450 m. Courtship
display flights lasted 60-900 sec (x = 334.7 ± 191.5
sec). Cartwheeling behavior or sky dancing (Good-
rich et al. 1996) was only observed three times by
three different pairs, in which the male was flying
on top of the inverted female with their talons ex-
posed. The birds proceeded to tumble with semi-
locked talons at high speeds until they reached the
forested canopy, where they quickly released their

December 2005

Puerto Rican Broad-winged Hawk Ecology

409

Table 2. Model selection: parameters (K), relative AIC^, Delta AIC (A,), Akaike Weights (w,), Goodness-of-Fit
statistic, P-value, and percent correct classification for Broad-winged Hawk nests in Rio Abajo Forest, Puerto Rico,
2001 - 02 ).

Model Selction

AIC,

P-VALUE

Percent

DBH + Canheight + Cliffwall + Overstems

20.057

0.000

0.304

10.953

0.027

77.8

DBH

21.362

1.305

0.158

6.613

0.010

66.7

Cliffwall

22.309

2.252

0.099

5.283

0.022

72.2

DBH + Canheight + Cliffwall

22.391

2.334

0.095

9.009

0.029

72.2

Nudds 2

22.399

2.342

0.094

5.762

0.016

61.1

DBH + Canheight

22.957

2.900

0.071

7.167

0.028

66.7

Aspect + DBH -1- Cliffwall

23.928

3.871

0.044

8.569

0.036

72.2

DBH + Canopy cover

24.619

4.562

0.031

6.765

0.034

61.1

Road + Cliffwall

25.591

5.534

0.019

5.582

0.061

72.2

Cliffwall + DBH

25.591

5.534

0.019

8.493

0.014

72.2

Midstems

26.050

5.993

0.015

3.018

0.082

55.6

Slope

26.974

6.917

0.010

2.346

0.126

66.7

Road

27.192

7.135

0.009

2.211

0.137

55.6

Canopy cover

27.435

7.378

0.008

1.977

0.160

55.6

Nudds 2 + Midstems + Overstems

27.961

7.904

0.006

8.146

0.043

61.1

Overstems

28.484

8.427

0.005

1.023

0.312

59.0

Midstems + Overstems

28.628

8.571

0.004

3.486

0.175

50.0

Canheight

28.862

8.805

0.004

0.650

0.420

38.9

DBH + Canheight + Cliffwall + Aspect

29.070

9.013

0.003

9.047

0.060

66.7

Aspect

29.458

9.401

0.003

0.066

0.797

0.0

Aspect + Slope

30.340

10.283

0.002

2.395

0.302

72.2

talon lock, swooped up, and dispersed upward in
separate directions.

Territorial flights were elicited by the presence
or vocalizations from intruding Red-tailed Hawks
and juvenile Broad-winged Hawks in the vicinity of
the residents’ territory. Flights varied in intensity
and depended on the intruding species and its
proximity to the nest. Generally, males were first
to fly and confront the intruder (Wiley and Wiley
1981). Adults used alarm vocalizations to warn
their mate of an intruding bird. During these dis-
plays, adults used stuttered and whistle squeal vo-
calizations (Burns 1911). Stuttered and whistle
squeals vocalizations were used in high-intensity
displays. When Red-tailed Hawks were detected.
Broad-winged Hawks responded quickly with rapid-
pursuit flights. Resident birds circled and soared
to an altitude above the intruding bird and re-
peatedly dived at it. The resident male continued
to dive at the intruder until the intruder departed
the territory. In some cases, the resident bird ex-
tended its talons during its dives. In one instance,
a male broadwing locked talons with an intruding
Red-tailed Hawk; once the intruder left the area,

the resident male silently dove or “parachuted”
back to its territory.

Dipping flight, or undulating display (Wiley and
Wiley 1981, Brown and Amadon 1989), was a com-
mon behavior used in all intense intruder inter-
actions in which the resident bird was successful at
chasing the Red-tailed Hawk. Territorial confron-
tations between conspecific neighbors were less
intense than toward Red-tailed Hawks. From the
radiotelemetry study, a radio of a juvenile Broad-
winged Hawk (5167) was found and all the feathers
were plucked (D. Hengstenberg and F. Vilella un-
publ. data). The cause of mortality was determined
to be a Red-tailed Hawk, which had been observed
numerous times in the same area as the juvenile
broadwing.

Perched intruders were generally attacked by a
slower supplantation flight (Wiley and Wiley 1981)
or a dive in which the intruder typically fled the
area. If the intruder remained, the residents then
circled above and used low angled dives until the
intruder departed (Wiley and Wiley 1981).

Nesting Biology. We found 10 nests during our
study in Rfo Abtyo Forest. Onset of incubation was

410

Hengstenberg and Vilella

VoL. 39, No. 4

Table 3. Broad-winged Hawk nests monitored during
the breeding seasons 2001 and 2002, Rio Abcgo Forest,
Puerto Rico.

Reproductive Variables

2001

2002

Both

Years

Number of nests found

Occupied nests

Failed nests

Successful nests

Proportion successful nests

0.83

0.50

0.70

Mayfield nest success

0.81

0.51

0.67

Number of nestlings

Number fledged

Nestling loss

0.14

0.33

0.20

Fledglings per nest

1.2

from 28 February-21 March in 2001 and from 6-
16 March in 2002. Hatching occurred from 9-20
April in 2001 and from 6-17 April in 2002. In 2001,
six juveniles fledged at 35-39 d between 2-25 May,
and two juveniles fledged at 35-36 d from 21-22
May in 2002. Three nests failed during the study
(Table 3) . Two of the failed nests were attributed
to heavy rains. The third nest was depredated by a
Red-tailed Hawk.

For 2001 and 2002, nest survival for the incu-
bation and nestling periods was 0.67 (Table 3).
The probability of surviving from nest initiation
through fledging was 0.81 in 2001 and 0.51 in
2002. For both years, the probability of nest surviv-
al during the incubation period was 1.0. {N = 10).
The number of fledglings per successful nest was
1.20 in 2001, 1.0 in 2002, and 1.14 for both years
combined (Table 1).

During the egg stage, females spent the majority
of time incubating. However, our results differ
from the available information (Raffaele 1989, U.S.
Fish and Wildlife Service 1997), as we documented
males engaged in all nesting duties, including in-
cubation. In some instances, males were observed
continuously incubating for >4 hr and overnight.
Adult Broad-winged Hawks frequently brought
green vegetation, especially Trichilia hirta, to the
nest. During incubation, vegetation may act as a
buffer between nest branches and eggs. Raptors
may use fresh greenery for concealment, to reduce
odors, and to avoid ectoparasites (Wimberger
1984, Sibley 2001).

Nest Monitoring and Prey Delivery. We recorded
5534 min of nest observations during the incuba-

tion stage and 8825 min through the nestling
stage. During the incubation period, females in-
cubated approximately 53% of the time and males
23%. We observed both male and female Broad-
winged Hawks incubating overnight. The nest was
not attended 15%, and an unknown adult incubat-
ed 9% of the time. During the nestling period, the
nest was not attended 69% of the time, females
attended 17%, and males attended 14% of the
time. As the nestlings matured, the female spent
less time at the nest (Lyons and Mosher 1987).

Prey deliveries away from the nest were relatively
common, with either member of the pair initiating
solicitation calls (Goodrich et al. 1996). The deliv-
ering adult, usually the male, would vocalize back
and forth until the incubating female flew off the
nest to where the male was perched (<50 m from
nest) to obtain the prey item. While one adult was
eating, the other would fly to the nest and brood.
Most prey deliveries during the nestling stage oc-
curred during the early morning to mid-afternoon
period.

We observed 60 prey items delivered to 7 of 10
monitored nests during the brood-rearing periods
of 2001 and 2002 (Table 4). Prey consisted of 35%
rats {Rattus , 27% lizards, 17% birds, 12% ma-
croinvertebrates, 7% unidentified prey, and 3%
snakes. Pooled prey items (large and small) varied
among the four time periods (F^av = 4.01, P =
0.024). More prey was delivered to nests during
early morning to mid-afternoon than early even-
ing. Daily prey deliveries were distributed as fol-
lows: 38% early morning, 40% late morning to mid
afternoon, 17% mid to late afternoon, and 5% late
afternoon to early evening. However, neither the
number of small prey items (F 327 = 2.83, P =
0.068), nor the number of large prey items (^ 3,27
= 2.80, P = 0.067) brought to nest sites, differed
over the course of the day. The earliest prey deliv-
ery was recorded at 0856 H, and the latest prey
delivery was observed at 1846 H. We calculated a
mean prey delivery rate of 0.38 prey (SE — 0.08)
items per chick per hour (range = 0.14—0.80).

Nesting Habitat. All nests were within 50 m of a
rock wall. Nests sites were generally found on
southwest facing slopes (x = 204°). Distance
among nests averaged 838.5 m (SE = 79.98, range
- 200-1455 m) in 2001 and 793.0 m (SE = 91.87,
411-1231 m) in 2002. Distance did not vary be-
tween years (^0 ~ 0.362, P = 0.720) . There was no
difference amongst visual estimations and clinom-
eter readings of nest tree heights when compared

December 2005

Puerto Rican Broad-winged Hawk Ecology

411

Table 4. Observed prey items delivered to Broad-winced Hawk nests or consumed in Rio Abajo Forest, Puerto Rico,
2001 - 02 .

Common Name

Taxonomic Name

Observed No.
OF Prey

Percent

Puerto Rican giant centipede

kjcuvujjt/vufu riuri '^

6.7

Puerto Rican arboreal millipede

Orthocricus arboreus

5.0

Melodius coqui

Eleutherodactylus wightmanae

1.7

Common coqui

Eleutherodactylus coqui

5.0

Common anole

Anolis cristatellus

3.3

Banded anole

Anolis stratulus

1.7

Yellow-breasted anole

Anolis gundlachi

3.3

Small green anole

Anolis evermanni

1.7

Orange dewlap anole

Anolis krugi

1.7

Snake anole

Anolis pulchellus

1.7

Green giant anole

Anolis cuvieri

3.3

Common gecko

Spaherodactylus macrolepis

3.3

Puerto Rican boa

Epicrates inoratus

1.7

Ground snake

Arrhyton exiguum

1.7

White-winged Dove

Zenaida asiatica

1.7

Bananaquit

Coereba flaveola

10.0

Puerto Rican Bullfinch

Loxigilla portoricensis

5.0

Common mouse

Mus musculus

20.0

Roof rat

Rattus rattus

11.7

Norway rat

Rattus norvegicus

3.3

Unidentified prey items

—

6.7

Total prey items

—

100

to actual tape-measured heights (P = 0.25). Nest
tree height averaged 22.3 ± 7.7 m (range = 16.0-

35.1 m) and nest height averaged 16.3 ± 5.6 m
(range = 10.0-25.9 m). Nest tree DBH averaged

46.1 ± 15.6 m (range = 23.0-74.5 cm). Dimen-
sions for the two nests measured were: 0.79 m
(long diameter) by 0.52 m (short diameter) by 0.61
m (depth), and 0.46 m (long) by 0.31 m (short)
by 0.61 m (depth). Nest cup depth measured 1.27
and 2.54 cm, respectively. Within nest site vegeta-
tion plots we recorded 13 species of overstory
trees, but only four tree species were used as nest
trees. Nests were in maria, Honduras mahogany,
moca, and guaraguao trees.

Of 27 microhabitat variables measured, five dif-
fered between nests and random sites (Table 1).
Nest sites were closer to cliff walls (t^Q = 2.578, P
= 0.020), had greater tree height = —3.020, P
= 0.008), larger DBH = -3.048, P = 0.008),
and denser understories at 1.5 m (ti 5 = —2.409, P
= 0.028) and 2.0 m = -2.742, P = 0.015) than
random sites.

Logistic regression produced a best nest site
model containing two variables: DBH (parameter

= 0.1800, SE = 0.0965, x^ = 3.4814, P = 0.062),
and Nudds 2 m (parameter = 0.1297, SE = 0.0865,
X^i = 2.2512, P = 0.134). This variable combina-
tion correctly classified Broad-winged Hawk nests
83.3% of the time (Table 5). The best AIC model
for nest sites contained DBH (parameter = 1.2853,
SE = 1.5429, xS = 0.694, P = 0.405), canopy
height (parameter = 5.5472, SE = 7.5492, x^i ~
0.5399, P = 0.540), distance to rock wall (param-
eter = -0.4281, SE = 0.8384, x^ = 0.2607, P =
0.610), and overstory stems (parameter = 2.6233,
SE = 3.5889, x^ = 0.5343, P = 0.465). These four
variables correctly classified nests 77.8% of the
time (Table 2).

Discussion

Albeit our small sample of nests, phenology was
similar across both years, with the onset of incu-
bation beginning in late February and juveniles
fledging by the end of May. The post-fledging de-
pendency period lasted 4—8 wk after the juveniles
left the nest. During the first 2-3 wk post-fledging,
juveniles frequently returned to the nest to receive

412

Hengstenberg and Vilella

VoL. 39, No. 4

Table 5. Variable selection of Broad-winged Hawk nest sites in Rio Abajo Forest, Puerto Rico, 2001-02. Significant
parameters (K), relative AIC (AICJ, Delta AIC (AJ, Akaike Weight (w*), Goodness-of-Fit statistic (x^), P-value, and
percent correct classification.

Variable Selection

AIC,

P-VALUE

Percent

DBH + Nudds 2

16.774

0.000

0.551

10.754

0.005

83.3

Cliffwall + DBH

19.386

2.612

0.149

8.493

0.014

72.2

Cliffwall + DBH -1- Nudds 2

19.630

2.856

0.132

11.553

0.009

83.3

DBH

21.362

4.588

0.056

6.613

0.010

66.7

Cliffwall + Nudds 2

21.770

4.996

0.045

8.595

0.014

83.3

Cliffwall

22.309

5.535

0.035

5.283

0.022

72.2

Nudds 2

22.399

5.625

0.033

5.762

0.016

61.1

prey deliveries from the adults and to roost for the
night.

Broad-winged Hawk nests in Puerto Rico aver-
aged 1.1 young per nest attempt and 67% nest suc-
cess. Our estimate is almost double what Delannoy
and Tossas (2002) reported (0.66 fledglings/nest)
for Broad-winged Hawk nests in Rio Abajo from
1994 to 1996. However, our estimates of nest suc-
cess and young per nest attempt were slightly lower
compared to Broad-winged Hawk studies in North
America (Armstrong and Euler 1983, Crocoll 1984,
Rosenfield 1984).

The number of fledglings per successful nest
and overall nest success was greater in 2001 than
in 2002. Lower nest success in 2002 may have been
attributed to rain events that occurred in April of
2002. Two nest sites were abandoned within the
same week of heavy rain in April 2002. Santana and
Temple (1988) reported lower success of Red-
tailed Hawks nesting in the eastern Luquillo Moun-
tains rainforest region during extensive rainy pe-
riods. Similarly, severe rainfall was suggested as a
cause of nest failures of the Puerto Rican Sharp-
shinned Hawk {Accipiter striatus vennator) in the Lu-
quillo Mountains (Snyder and Wiley 1976) and in
forests of the central mountain range of the island
(Delannoy and Cruz 1988).

April and May are important months to nestling
survival. During this time period, Broad-winged
Hawks are brooding partially feathered nestlings.
In 2001, total precipitation from April and May was
44.2 cm. Conversely, April-May precipitation in
2002 was 54.4 cm. April rains in 2002 coincided
with the presence of recently-hatched chicks or
young nestlings and may have caused nest aban-
donment and hypothermia of young at the two
failed nests.

At Rio Abajo Forest, Broad-winged Hawks for-

aged primarily on rats, lizards, and small birds (Ta-
ble 4) . The Broad-winged Hawk is an opportunistic
feeder who forages on a wide variety of prey (Rush
and Doerr 1972, Reran 1978). However, our in-
ability to detect a daily pattern of prey deliveries
may have been a result of our small sample of nests
and prey delivery observations.

Prey size or type exploited at Rio Abajo Forest
may be a function of seasonality (wet vs. dry), as
changing weather conditions may produce differ-
ences in dietary patterns (Grubb 1977, Stinson
1980). In tropical environments such as Puerto
Rico, rain may limit foraging opportunities (Foster
1974). We observed Broad-winged Hawks at Rio
Abajo Forest were less active during periods of
rain.

There was no difference in the spatial distribu-
tion of nest sites between years, suggesting Broad-
winged Hawks may maintain territories year round.
These clusters of nests (Fig. 1) are bounded by
limestone ridges and cliff walls, where pairs soar
along their respective ridge tops. This may have
some advantages. Pairs may be better able to detect
intruding Red-tailed Hawks. Vigilance may contrib-
ute to greater survival of nesting birds (Alcock
1993).

Breeding Broad-winged Hawks were aggressive
and successfully deterred intruding Red-tailed
Hawks from their nesting territories. Delannoy and
Tossas (2002) speculated similar nest-site require-
ments between Broad-winged Hawks and Red-
tailed Hawks could lead to aggressive encounters.
However, we found no evidence of nesting by Red-
tailed Hawks within the closed canopy forests of
Rio Abajo. By and large, Broad-winged Hawk court-
ship and territory defense behavior in Puerto Rico
was similar to that of the Ridgway’s Hawk {Buteo

December 2005

Puerto Rican Broau-winged Hawk Ecology

413

ndgwayi) in moist limestone forests of the Domin-
ican Republic (Wiley and Wiley 1981).

Territory occupancy seemed relatively stable be-
tween years. The year-round residency and site fi-
delity of Broad-winged Hawks in the moist lime-
stone region of Puerto Rico may be indicative of
long-term pair bonds (Griffin et al. 1998). Like
other tropical raptors (Mader 1982, Griffin et al.
1998), the subspecies in Puerto Rico seems to ex-
hibit high site fidelity (73%, N — 11),

Our results from radio-marked breeding birds
(D. Hengstenberg and F. Vilella unpubl. data) sug-
gest Broad-winged Hawks tend to nest in the same
stand or nearby from one year to the next (Reran
1978). We observed courtship behavior in 15 ad-
ditional pairs, but found no evidence of nests or
nest building. This may suggest that while some
pairs may hold nesting territories, they do not nec-
essarily build a nest or lay eggs every year, as has
been documented in other raptors (Steenhof
1987).

Five nests constructed in maria trees were placed
atop termite nests in the main crotch of the tree.
Broad-winged Hawks nesting in North America
sometimes place their nest on top of old bird and
squirrel nests (Goodrich et al. 1996).

Distance to cliff wall, tree height and DBH,
Nudds board 1.5 m, and Nudds 2.0 m differed be-
tween nest and random sites. Variables DBH and
Nudds 2 m best classified nest sites, suggesting that
Broad-winged Hawks at Rio Abajo Forest may pre-
fer large trees and dense understories (Table 5).
Also, Broad-winged Hawks in North America avoid-
ed smaller trees and selected large DBH trees (Ti-
tus and Mosher 1987). At Rio Abajo Forest, nest
sites had denser understories than random sites.
Dense understories may be related to prey avail-
ability for adults. These dense understories may of-
fer fledglings protection from predators and great-
er foraging opportunities of prey. Radio-marked
adults and juveniles were frequently observed
hunting in the dense understory around their nest
sites. Foraging habitat studies have suggested
Broad-winged Hawks select sites with high prey
availability (Steblein 1991). However, further re-
search is required to better understand the rela-
tionships between Broad-winged Hawks in Rio Aba-
jo Forest and prey populations.

Model selection procedures for nests (site spe-
cific) yielded a four-variable model in which DBH,
canopy height, cliff wall, and overstory stems cor-
rectly classified nest sites (Table 2). This suggests

closeness to karst cliff walls and canopy height may
be additional predictors of Broad-winged Hawk
nest habitat, in addition to basal area (i.e., DBH)
and understory cover.

Nest tree height averaged 22.2 m, whereas can-
opy heights of nest plots averaged 17.9 m and ran-
dom sites averaged 16.6 m, suggesting Broad-
winged Hawks select emergent trees for their nests.
Our results coincide with nest site characteristics
of North American broadwings (Goodrich et al.
1996). Delannoy and Tossas (2002) reported a
mean nest tree height of 27.0 m and a mean can-
opy height of 15.7 m. On average, nest heights in
Puerto Rico were taller than nest heights reported
from North America (Burns 1911, Matray 1974, Ti-
tus and Mosher 1981, Armstrong and Euler 1983,
Rosenfield 1984). This may reflect the relative
lengths of trees in tropical versus temperate forests
(Fedorov 1966).

Broad-winged Hawk nest sites were located with-
in 50 m of a cliff wall. In the karst region, cliff walls
are very abundant. Cliff walls may offer nest sites
with adequate protection from the elements (wind,
rain, and sun), intruding predators, provide van-
tage points, and facilitate reduction in energy re-
quirements when searching for thermal updrafts.
Nests sites were generally found on slopes facing
southwest (x = 204°). This nest placement may
help protect the nests from the prevailing easterly
winds. Broad-winged Hawk nest sites in a limestone
forest may be described as occurring in mature
closed-canopy overstory stands sheltering a thin
midstory, a dense understory, and in close prox-
imity to a cliff wall.

Conservation and persistence of the breeding
population of Rio Abajo Forest may depend on
management of the existing forest stands used by
Broad-winged Hawks. Further research is required
in Rio Abajo Forest to increase sample sizes of nest
sites and validate the broadwing-habitat relation-
ships revealed by our habitat model. Moreover, var-
iance estimates of parameters from our study will
provide baseline information needed to calculate
sample sizes for future research. We suggest addi-
tional studies to quantify broadwing habitat in oth-
er localities of the karst region and to develop hab-
itat models at multiple spatial scales.

At Rio Abajo Forest, managers should limit dis-
turbance within valleys used by broadwings during
the critical nest initiation and incubation periods
(i.e., February to April). Based on our preliminary
results on habitat relationships, silvicultural prac-

414

Hengstenberg and Vtt.et.ia

VoL. 39, No. 4

tices within Rio Abajo Forest that promote main-
tenance of canopy emergent trees and dense un-
derstories may improve habitat conditions for
nesting pairs as well as fledglings during their de-
pendence period. Moreover, Broad-winged Hawks
readily used plantation tree species such as maria
and Honduras mahogany for nest sites. We rec-
ommend the DNER Forest Service encourage sur-
rounding private landowners to engage in agrofor-
estry practices using these fast-growing plantation
species. Additionally, programs for private lands
that promote maintenance and enhancement of
forest cover (e.g., USFWS Partners for Wildlife)
should be brought to the attention of the land-
owners adjoining Rio Ab^o Forest.

In an attempt to establish a second wild popu-
lation, releases of captive-reared Puerto Rican Par-
rots are scheduled for 2006 (U.S. Fish and Wildlife
Service 1999). Available information suggests
Puerto Rican Parrots may exceed the size of avian
prey taken by Broad-winged Hawks (Snyder and
Kepler 1987). At Rio Abajo, 61% of prey deliveries
to nests were rodents and Anolis lizards (Table 4) .
Forest songbirds (e.g., Puerto Rican Bullfinch [Lo-
xigilla portoricensis] and Bananaquit [ Coereba flaveo-
la] ) were the avian prey taken (Table 4) .

In contrast, Red-tailed Hawks are known parrot
predators (White et al. 2005) . However, our results
indicated resident Broad-winged Hawks chased off
intruding Red-tailed Hawks effectively in Rio Abajo
Forest. Owing to the likely negative relationship
between these sympatric Buteos, resident Broad-
winged Hawks in Rio Abajo may indirectly provide
some degree of protection to released parrots from
predation by excluding intruder Red-tailed Hawks.
However, research is required to examine the re-
lationship between spatial overlap of parrots and
broadwings and the likelihood of Red-tailed Hawk
predation on released parrots.

Other studies have reported some avian species
select nest sites close to more aggressive species
that regularly attack or mob predators (Durango
1949, Clark and Robertson 1979, Wiklund 1979,
Dyrcz et al. 1981, Norrdahl et al. 1995). The Wood-
pigeon {Columba palumbus) benefits from nesting
in association with Eurasian (northern) Hobbies
(Falco subbuteo; Bogliani et al. 1999).

Nevertheless, both the Puerto Rican Parrot and
Broad-winged Hawk are listed as endangered (U.S.
Fish and Wildlife Service 1997, 1999). Therefore,
a co-management approach will be required to en-
sure habitat management activities for one species

are not done at the expense of the other. We rec-
ommend parrot habitat management activities
(i.e., deployment of artificial cavities) should be
limited to the nonbreeding season (August-De-
cember) to minimize disturbance to Broad-winged
Hawk nesting pairs and post-fledging dependent
juveniles.

Ultimately, the future of both these endangered
species rests on the ability to disseminate research
results to forest managers and policymakers. This
information in turn will help to guide the protec-
tion and conservation of the karst forest region of
Puerto Rico, as further forest fragmentation will
impact severely the recovery of both the broadwing
and the parrot. Multiagency efforts are underway
to acquire and protect a significant portion
(>30 000 ha) of forest in the moist karst region of
Puerto Rico (Lugo et al. 2001). Broad-winged
Hawks do not limit their activities to the Rio Abajo
Forest boundaries, and their fate in the surround-
ing private lands may be uncertain. Therefore,
DNER forest managers should work proactively
with the surrounding land owners to promote
land-use practices to conserve and to enhance ex-
isting forest cover. Future patterns of land use
around the forest boundary may indirectly and di-
rectly affect the ability of the Rio Abajo Forest to
function as an effective conservation unit for the
Broad-winged Hawk.

Acknowiedgments

Funding was provided by the USFWS, Caribbean Field
Office. The DNER Forestry Division provided access to
Rio Abajo Forest. We are indebted to J. Casanova, DNER
Management Officer at Rio Abajo Forest, and his staff
for providing assistance and logistic support. The DNER
Terrestrial Resources Division provided housing facilities
at Rio Abajo Aviary. We are grateful to I. Llerandi, J. Rios,
and A. Jordan for field assistance. Thanks to student vol-
unteers from the University of Puerto Rico at Arecibo
and Utuado. We are grateful for the helpful comments
of C. Delannoy on the raptors of Puerto Rico. We thank
J. Bednarz, K. Bildstein, L. Goodrich, K. Titus, and J. Wi-
ley for suggestions that greatly improved earlier versions
of the manuscript. Animal collection and handling pro-
cedures were conducted under the auspices of DNER
permit Ol-EPE-019, Master Station Permit 22456 of the
USGS Bird Banding Laboratory, and Mississippi State
University’s Institutional Animal Care and Use Commit-
tee protocol No. 00-094.

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Received 28 June 2004; accepted 27 August 2005

J. Raptor Res. 39(4):417-428
© 2005 The Raptor Research Foundation, Inc.

RAPTOR ABUNDANCE AND DISTRIBUTION IN THE LLANOS

WETLANDS OF VENEZUELA

Wendy J. Jensen, 1 Mark S. Gregory, and Guy A. Baldassarre

State University of New York, College of Environmental Science and Forestry, 1 Forestry Drive,

Syracuse, NY 13210 US. A.

Francisco J. Vilella

uses Biological Resources Division, Cooperative Research Units, Department of Wildlife and Fisheries,

Box 9691, Mississippi State, MS 39762-9691 U.S.A.

Keith L. Bildstein

Acopian Center for Conservation Fearning, Hawk Mountain Sanctuary, 410 Summer Valley Road,

Orwigsburg, PA 17961 U.S.A.

Abstract. — The Llanos of Venezuela is a 275 OOO-km® freshwater wetland long recognized as an impor-
tant habitat for waterbirds. However, litde information exists on the raptor community of the region.
We conducted raptor surveys in the Southwestern and Western Llanos during 2000-02 and detected 28
species representing 19 genera. Overall, areas of the Llanos that we sampled contained 52% of all raptor
species and more than 70% of the kites, buteos, and subbuteos known to inhabit Venezuela. Regional
differences in the mean number per route for four of the 14 most common species, the Crested Ca-
racara ( Caracara plancus ) , Black-collared Hawk {Busarellus nigricollis) , American Kestrel {Falco sparverius) ,
and Osprey (Pandion haliaetus), were significant {P < 0.0018) in relation to the wet or dry seasons. Of
the 14 less common species, six were detected in only one season (wet or dry). The Southwestern and
Western regions of the Llanos support a rich raptor community composed primarily of nonmigratory
wetland-dependent and upland-terrestrial species.

Key Words: Neotropics-, Venezuela, Llanos, savanna, wetlands', roadside surveys.

DISTRIBUCION YABUNDANCIA DE RAPACES EN HUMEDALES DE LOS LLANOS DE VENZUELA

Resumen. — Los llanos de Venezuela constituyen un humedal de agua dulce de 275 000 km^ que ha sido
tradicionalmente reconocido como un ambiente importante para las aves acuaticas. Sin embargo, existe
poca informacion sobre la comunidad de rapaces de la region. Realizamos censos de aves rapaces en
el sudoeste y el oeste de los llanos entre 2000 y 2002 y detectamos 28 especies que representaron 19
generos. En total, las areas de los llanos que censamos contuvieron el 52% de todas las especies de
rapaces y mas del 70% de los elanios, buteos y subbuteos que habitan en Venezuela. Las diferencias
regionales en el numero medio por ruta para cuatro de las 14 especies mas comunes, Caracara plancus,
Busarellus nigricollis, Falco sparverius y Pandion haliaetus, fueron significativas (P< 0.0018) con relacion a
las estaciones humeda y seca. De las 14 especies menos comunes, seis fueron detectadas en una sola
estacion (humeda o seca). Las regiones del sudoeste y del oeste de los llanos albergan una rica comu-
nidad de aves rapaces compuesta primariamente por aves no migratorias que dependen de humedales
y de especies terrestres de lugares elevados.

[Traduccion del equipo editorial]

South America comprises 12% of the world’s
land surface, yet supports 28% of all raptors (Bie-
rregaard 1998). Most South American raptors do
not appear threatened globally, but more infor-
mation is needed to confirm current assessments

^ Email address: wjjensen@syr.edu

and appropriately address threats (Bierregaard
1998, Bildstein et al. 1998). Community level rap-
tor research in South America has been primarily
focused in forest habitats (e.g., Thiollay 1984,
Thiollay 1989, Alverez et al. 1996, Manosa and Pe-
drocchi 1997, Manosa et al. 2003); thus, little is
known about the raptor populations within the ex-

417

418

Jensen et al.

VoL. 39, No. 4

tensive savanna and grassland regions of the con-
tinent. Raptor surveys in nine South American
countries during 1979 detected the greatest num-
ber of species in the savannas, mixed riparian for-
ests, pastures, and open areas of interior Venezuela
(Ellis et al. 1990), indicating that these areas are
important habitats for South American raptors.
Furthermore, Neotropical raptors of open land
and savanna habitats are currently threatened by
habitat loss, including wetland depletion and land-
scape homogenization (Alvarez-Lopez and Kattan
1995).

In Venezuela, the savannas of the interior are
part of an extensive (275 000 km^) wetland com-
plex called the Llanos. The Llanos cover approxi-
mately 31% of Venezuela (Mittermeier et al. 2003)
and are located in the latitudinal region character-
ized by the greatest avian endemism in the North-
ern Hemisphere (Bibby et al. 1992). Between 32-
36 nonmigratory and North American migratory
raptor species use some or all of the Llanos (Fer-
guson-Lees and Christie 2001, Hilty 2003). Al-
though the natural history, biology, and habitat as-
sociations of some of these species have been
studied locally (Mader 1981, 1982, Beissinger et al.
1988, Balgooyen 1989, Kirk and Currall 1994),
community based, landscape-level surveys are lack-
ing.

Our objective was to document and compare the
species richness, relative abundance, and distribu-
tion of nonmigratory and migratory raptors in the
savannas of the Southwestern and Western regions
of the Venezuelan Llanos. We also compared these
population parameters between the distinct wet
and dry seasons that characterize the Llanos.

Study Area

Venezuela supports 1381 species of birds (Hilty 2003)
and is considered a globally important region of biodi-
versity in part due to its rich avifauna (Mittermeier and
Mittermeier 1997, Myers et al. 2000), The Venezuelan
Llanos is located between ca. 6-9°N and 63— 71 TV and is
bordered by the Coastal Cordillera to the north, the Ori-
noco Delta and Guiana Shield to the east and southeast,
Colombia to the south and southwest, and by the Andes
Mountains to the northwest.

Annual rainfall in the Venezuelan Llanos ranges from
90-180 cm (Silva and Moreno 1993), with most rain fall-
ing and widespread flooding occurring from April
through November (Cole 1986). In contrast, the late No-
vember-late April dry season typically is rain free (Troth
1979).

The Venezuelan Llanos is divided into three general
areas: western, central, and eastern (Huber and Alcaron
1988). Covering 90 000 km‘^, the western area comprises

35% of the freshwater wetland in Venezuela and spans
north and west of the Orinoco River from ca. 69-7l°W
and 6-9°N (Bulla et al. 1990). This area is relatively flat,
with elevation ranging from sea level at the Orinoco Riv-
er to 155 m near the foothills of the Andes. The western
area is further divided into two distinct regions known as
the Southwestern and Western Llanos (Fig. 1; Huber and
Alcaron 1988).

The Southwestern Llanos includes the vast open-sa-
vanna-wetland habitats that extend from the Meta and
Orinoco rivers northwest to the agricultural-savanna-for-
est mosaic habitats of the Western Llanos. The South-
western Llanos is characterized by poor soils, savanna
habitats with small patches of trees, gallery forest, and
extensive wet season flooding that renders the region
largely unsuitable for agriculture (Huber and Alcaron
1988).

The Western Llanos encompasses the alluvial plains
bordered by the foothills of the Andes and extends south-
east to the open savannas of the Southwestern Llanos.
This region is characterized by fertile soils and partial
flooding that support agricultural production and native
forests dominated by tree species similar to those of the
Amazon basin (Huber and Alcaron 1988, Silva and Mo-
reno 1993).

Methods

Sampling Design. We surveyed raptors along the sparse
network of roads accessible during both the wet and dry
seasons in the Southwestern and Western Llanos (Fig. 1)
Despite limitations inherent in roadside surveys (Millsap
and LeFranc 1988, Bunn et al. 1995), such counts can be
used to survey relative raptor abundance, community
composition, and habitat associations across large land-
scapes (Woffinden and Murphy 1977, Thiollay 1978, Ellis
et al. 1990, Sorley and Andersen 1994, Seavy and Apo-
daca 2002). However, roadside surveys in open habitats
may be inadequate for detecting small and uncommon
raptor species unless surveys incorporate frequent and
regular stops (Whitacre and Turley 1990). Therefore, we
used the North American Breeding Bird Survey model
(Droege 1990) to establish stationary surveying points
along road routes.

We placed 50 survey routes along roads where the over-
all distribution of survey routes was dictated by accessi-
bility of roads during the wet season (Fig. 1). Each route
was 22.5 km long with 16 sample points spaced 1.5 km
apart (Jensen 2003: Appendix A) . Each sample point was
surveyed by a 2-person surveying team for 3 min to the
right and left side of the road for a total of 6 min/ point.
All raptors were tallied within a 500-m radius as measured
by rangefinder binoculars. Except for the King Vulture
{Sarcoramphus papa), we did not tally Cathartid vultures.
Scientific and common names of birds follow Ferguson-
Lees and Christie (2001).

Raptors were surveyed during rainless periods of the
day, primarily from 0700-1200 H, and never later than
1400 H. Surveys were conducted over ca. 6-wk periods
twice each year between August 2000 and March 2002
The 6-wk periods coincided with the end of the wet (Au-
gust-October) and dry seasons (January-March). We
surveyed 27 routes in the wet season of 2000, 39 in the

December 2005

The Raptor Community of the Llanos

419

North Central Llanos

Central

Western Llanos

Llanos

Southwestern Llanos

Legend

c j Regions of the Venezuelan Llanos
n The Colonijian L i^nos

crwTis

10°N

8"N

6"N

70" W

68" W

66"Vy

Figure 1. Study area map of the raptor survey during wet seasons 2000 and 2001 and dry seasons 2001 and 2002
in the Southwestern and Western Llanos of Venezuela. Route clusters are areas where groups of survey routes con-
taining sample points are located.

420

Jensen et al.

VoL. 39, No. 4

dry season of 2001, 50 in the wet season of 2001, and 50
in the dry season of 2002 .

Analysis. We calculated the total number of individuals
detected on all surveys, as well as species totals, percent
composition, and frequency of detection. We classified
percent composition into four species abundance classes:
Very common (10-26% of all individuals detected), Com-
mon (3-5%), Uncommon (1-2%), and Rare (<1%). We
used Estimates Version 6 . Obi software (Colwell 2000) to
generate a species accumulation curve to evaluate the
probability that our 2-yr 50-route roadside survey design
was adequate for documenting all detectable raptor spe-
cies.

We then calculated the mean number of individuals
per species per route (mean number per route) by year,
season, and region to investigate annual changes in abun-
dance between the 2000 and 2001 wet seasons and the
2001 and 2002 dry seasons for each region. For this com-
parison we used the 27 routes surveyed during the first
survey visit (wet season 2000 ) and resurveyed for the du-
ration of the survey (2001 and 2002): Southwestern Lla-
nos (15 routes) and Western Llanos (12 routes). Rare
abundance class species were detected in numbers too
low to meet the underlying assumptions for a /-test and
were omitted from all subsequent statistical tests. For the
14 most common species, we used paired /-tests to eval-
uate four hypothesis (Hoj: mean number per route
Southwestern Llanos wet season 2000 = mean number
per route Southwestern Llanos wet season 2001; Hog:
mean number per route Southwestern Llanos dry season
2001 = mean number per route Southwestern Llanos dry
season 2002; Hog: mean number per route Western Lla-
nos wet season 2000 = mean number per route Western
Llanos wet season 2001; H 04 : mean number per route
Western Llanos dry season 2001 = mean number per
route Western Llanos dry season 2002). Differences were
considered significant at L* < 0.10 because we were in-
terested in large-scale broad patterns. However, we used
the Bonferroni Method to control for inflated experi-
mentwise type I error rate resulting from simultaneous
multiple comparisons (Beal and Khamis 1991). For all
analysis, Bonferroni corrected significance for 56 com-
parisons was determined at {P < 0.0018).

We then combined data from both years to investigate
seasonal and regional differences in species numbers,
species diversity, community composition, and mean
number per route for each species. During the 2-yr study,
50 routes were surveyed (Southwestern Llanos 28 routes,
Western Llanos 22 routes) . We surveyed 27 routes during
both survey years (wet season 2000 and dry season 2001 )
and an additional 23 routes during the second survey
year (wet season 2001 and dry season 2002). To stan-
dardize the number of individuals detected on the 27
routes surveyed over 2 -yr, we averaged the number of
individuals per survey point across survey years for each
species. We then combined this 27-route average with the
data from the 23 routes surveyed only during the second
survey year to yield 50 total routes. Comhining the data
using this method preserved the majority of data collect-
ed, accounted for variation in numbers of individuals de-
tected for each species on routes replicated over survey
years, and preserved data from routes surveyed only dur-
ing the second year.

We calculated species numbers and Simpson’s Inverse
Diversity Index (D = 1/X pi^) for the wet and dry seasons
within each region (Hayek and Buzas 1996). We also cal-
culated Jaccard’s Coefficient of Community Similarity to
estimate the percent overlap between communities in
both seasons and regions (Magurran 1988). Again, we
used Estimates version 6.0b 1 software (Colwell 2000) to
generate species accumulation curves for each regional
and seasonal dataset to evaluate the probability that the
number of routes surveyed in each region for each sea-
son were adequate for documenting all detectable raptor
species.

To investigate seasonal and regional differences in
numbers for each species, we first calculated the mean
numbers per route for each region and season. To com-
pare seasonal di ff erences in mean numbers per route for
the 14 most abundant species, we used paired /-tests to
evaluate two hypothesis (Hop mean number per route
Southwestern Llanos wet seasons = mean number per
route Southwestern Llanos dry seasons; Hog: mean num-
ber per route Western Llanos wet seasons = mean num-
ber per route Western Llanos dry seasons). For the same
14 species, we also used 2-sample /-tests to evaluate re-
gional differences in mean numbers per route (Hop
mean number per route Southwestern Llanos wet sea-
sons = mean number per route Western Llanos wet sea-
sons; Hog: mean number per route Southwestern Llanos
dry seasons = mean number per route Western Llanos
dry seasons). The 14 rare abundance class species are
presented only as present or absent for each region and
season.

Results

General Patterns. We counted 5735 raptors rep-
resenting 28 species and 19 genera (Table 1). The
four most abundant species, Crested Caracara ( Ca-
racara plancus). Yellow-headed Caracara (Milvago
chimachima) , Savanna Hawk {Buteogallus meridiona-
lis), and Roadside Hawk (Buteo magnirostris) , com-
prised 72% of all individuals and were seen on 98-
100% of all routes. Four additional species were
classified as common and together comprised 15%
of all individuals. These were the Black-collared
Hawk {Busarellus nigricollis) , White-tailed Hawk
{Buteo albicaudatus) , Snail Kite {Rostrhamus sociabi-
lis) , and American Kestrel {Falco sparverius) . Six ad-
ditional species were uncommon and represented
10% of all detections. They were the Aplomado
Falcon {Falco femoralis) , Great Black Hawk {Buteo-
gallus urubitinga), White-tailed Kite {Elanus leucu-
rus) , Crane Hawk ( Geranospiza caerulescens) , Laugh-
ing Falcon {Herpetotheres cachinnans), and Osprey
{Pandion haliaetus). Fourteen additional species
comprised the remaining 3%. Species classified as
common were detected on 52-84% of all routes,
whereas uncommon species were detected on 44-
78% routes. The 14 rare species were detected on

December 2005

The Raptor Community of the Lianos

421

Table 1. Species detected during raptor surveys in the Southwestern and Western Llanos of Venezuela during wet
seasons in 2000 and 2001 and dry seasons in 2001 and 2002. Species are listed in order of relative abundance based
on percent composition. English common names and taxonomy follow Ferguson-Lees and Christie (2001).

Relative

Abundance

Class"'

Species

Status'^

Total

Number

Percent

Composition

Frequency

Occurrence

(%)<=

Very common

Creasted Caracara ( Caracara plancus)

1473

100

Yellow-headed Caracara {Milvago chimachima)

1061

100

Savanna Hawk {Buteogallus meridionalis)

1005

Roadside Hawk {Buteo magnirostris)

604

Common

Black-collared Hawk {Busarellus nigticollis)

269

Snail Kite {Rostrhamus sodabilis)

226

American Kestrel {Falco sparverius)

R/NAM

183

White-tailed Hawk {Buteo albicaudatus)

155

Aplomado Falcon {Falco femor alls)

113

Uncommon

Great Black Hawk {Buteogallus urubitinga)

110

White-tailed Kite {Elanus leucurus)

137

Crane Hawk {Geranospiza caerulescens)

Laughing Falcon {Herpetotheres cachinnans)

Osprey {Pandion haliaetus)

NAM

Rare

King Vulture ( Sarcoramphus papa)

0.7

Harris’s Hawk {Parabuteo unidnctus)

0.5

Grey-lined Hawk {Buteo nitidus)

0.5

Zone-tailed Hawk {Buteo albonotatus)

0.3

Slender-billed Kite {Rostrhamus hamatus)

0.3

Bat Falcon {Falco rufigularis)

0.3

Plumbeous Kite {Ictinia plumbea)

0.2

Hook-billed Kite ( Chondrohierax undnatus)

0.08

Long-winged Harrier {Circus buffoni)

0.09

Common Black Hawk {Buteogallus anthradnus)

0.09

Peregrine Falcon {Falco peregrinus)

NAM

0.09

Short-tailed Hawk {Buteo brachyurus)

0.09

Grey-headed Kite {Leptodon cayanensis)

0.05

Pearl Kite ( Gampsonyx swainsonii)

0.05

® Relative abundance class: Very common = 10-26% of all individuals detected; Common = 3-5%, Uncommon = 1-2%, Rare =
< 1 %.

^ Status: R = nonmigratory population, NAM = North American migratory population, R/NAM = nonmigratory and North American
migratory populations.

Frequency of occurrence: the percent of routes on which a species was detected.

<32% of all routes. There were three species of
North American migrants: Osprey, American Kes-
trel, and Peregrine Falcon {Falco peregrinus). The
Osprey and Peregrine Falcon combined comprised
1.2% of all individuals seen. In contrast, the Amer-
ican Kestrel comprised 3%, having both nonmigra-
tory and migratory populations (Hilty 2003). At
least one of these three species was seen at least
once on 82% of routes.

The species accumulation curve indicated the
number of routes surveyed over the two survey
years was adequate for documenting all species de-
tectable by roadside point count surveys in the

study area (Fig. 2) . Specifically, all 28 species were
detected with 34 routes (68% of all routes sur-
veyed) .

Yearly Comparisons. Among the 14 most com-
mon species there were no regional or seasonal
differences (P > 0.0018) in mean number per
route between survey years (Table 2).

Regional and Seasonal Patterns. The greatest
number of species, 25, was detected in the South-
western Llanos during the wet season and in the
Western Llanos during the dry season (Fig. 3) . Al-
though species numbers were equal between re-
gions, diversity was higher in the Western Llanos

422

Jensen et al.

VoL. 39, No. 4

Nutnbar of Routes Surveyed

Figure 2. Species accumulation graph of raptor species
detected on 50 survey routes in the Southwestern and
Western Llanos of Venezuela during the wet seasons in
2000 and 2001 and dry seasons 2001 and 2002.

during both seasons. Species accumulation curves
indicated the number of routes surveyed during
each season was adequate to detect the majority of
species for both regions (Fig. 4) .

The raptor community (Jaccard’s Coefficient of
Community Similarity) in the Southwestern versus
Western Llanos differed by 12%, both in the wet
and dry seasons. For seasons combined, 25 species
were detected in each region, of which 22 species
were shared between regions. The seasonal chang-
es in community composition within regions
(26%) were greater than the regional differences
within the wet and dry season (12%).

Four of the 14 most common species exhibited
regional differences {P< 0.0018) in mean number
per route in relation to the wet or dry seasons (Ta-
ble 3). The Crested Caracara (P < 0.001) and Os-
prey (P < 0.001) were more numerous in the
Southwestern Llanos than the Western Llanos dur-
ing the wet season. The Black-collared Hawk (P =
0.001) was more numerous in the dry season in
the Southwestern Llanos than the Western Llanos,
whereas the American Kestrel (P = 0.001) was
more numerous in the dry season in the Western
Llanos than the Southwestern Llanos.

Of the 14 rare species, six were detected only
during one season or region (Table 4). The Pere-
grine Falcon and Grey-headed Kite were seen only
in the dry season, and the Pearl Kite and Slender-
billed Kite were seen only in the wet season. The
Common Black Hawk was detected only in the
Southwestern Llanos in the wet season, and the
Plumbeous Kite was detected only in the Western
Llanos in the dry season.

Discussion

General Findings. The savannas of the South-
western and Western Llanos of Venezuela are par-
ticularly rich in raptors, supporting 52% (32 of 61)
of all regularly occurring migrant and resident spe-
cies found in Venezuela (Hilty 2003) . Indeed, dur-
ing our 2-yr study of the Venezuelan Llanos, these
regions included 55% of all hawk species (10 of
18), 70% (7 of 10) of kite species, 67% (4 of 6) of
vulture species, and 50% (3 of 6) of the regularly
occurring North American migratory species
(Hilty 2003). However, although the Llanos sup-
ported species assemblages equivalent to all other
Venezuelan life zones for most raptors, we did not
detect any of the eight eagle species that occur in
Venezuela.

Except for the three common Cathartid species
we did not count, we detected 24 of 27 resident
species expected to occur in the Llanos (Hilty
2003) . We did not detect three uncommon forest-
dwelling raptors thought to occur in the region:
the Collared Forest-Falcon (Micrastur semitorqua-
tus). Bicolored Hawk {Accipiter bicolor), and Ornate
Hawk Eagle (Spizaetus ornatus). We likely failed to
see these species because of the inherent difficulty
of detecting forest-dwelling species from roadside
surveys (Millsap and LeEranc 1988).

Of the three North American migrant species we
detected, two occur year-round in the Llanos. The
American Kestrel occurs year-round in the Llanos
because there are nonmigratory and migratory
populations (Hilty 2003) . Although the Osprey
population is wholly migratory, the Osprey occurs
year-round in the Llanos because first-year birds
reaching the Llanos remain for at least 18 mo
(Martell et al. 2001, Hilty 2003).

North American migratory species not seen dur-
ing surveys were the Northern Harrier {Circus cya-
neus), Broad-winged Hawk {Buteo platypterus) ,
Swainson’s Hawk {B. swainsoni), and Merlin {Falco
columbarius) . However, one Merlin was detected in
the Llanos, but not on survey routes. Historical
sightings of the Swainson’s Hawk and Northern
Harrier in the Llanos are considered accidental
(Hilty 2003), and satellite-tracking of Swainson’s
Hawks confirms that their migrations to and from
Argentina occur along the central and eastern
slopes of the Andes (Euller et al. 1998) . The Broad-
winged Hawk is thought to winter in portions of
the Llanos west and north of our study area (Hilty
2003).

December 2005

The Raptor Community of the Llanos

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423

424

Jensen et al.

VoL. 39, No. 4

Figure 3. Raptor species numbers and diversity in the
Southwestern and Western Llanos of Venezuela for com-
bined years during the wet season (2000 and 2001) and
the dry season (2001 and 2002).

Number of Routes Surveyed

Figure 4. Species accumulation graphs for raptors de-
tected in the Southwestern and Western Llanos of Ven-
ezuela for combined years during the wet seasons (2000
and 2001) and the dry seasons (2001 and 2002).

Overall, the Southwestern and Western regions
of the Llanos lacked the eagle diversity character-
istic of African savannas (Thiollay 1978). Nonethe-
less, these Llanos regions supported numbers of
raptor genera (21) similar to those found in the
seasonally-flooded savannas and agricultural-forest

mosaic habitats of Kidepo Valley National Park of
Uganda (22; Thiollay 1978). Consequently, migra-
tory species in the Southwestern and Western Lla-
nos only comprise a small portion of the raptor
community (7%), whereas migratory species ac-
count for 33% of the raptor community in Kidepo
Valley National Park of Uganda.

Table 3. Relative abundance of species and mean number of individuals (± SE) detected per route (mean/route)
during raptor surveys for combined years in the wet (2000 and 2001) and the dry season (2001 and 2002) in the
Southwestern and Western Llanos of Venezuela.

Relative

Abundance

Class*

Southwestern (N = 28) Western {N = 22)

Species Status*’ Wet'^ DrV Wet^ DrV'

Very common

Crested Caracara

10.21

1.37^

13.80

H-

1.88

2.98

± 0.88^

6.00

1.62

Yellow-headed Caracara

6.09

0.70

6.70

0.74

5.21

± 0.97

8.05

H-

1.25

Savanna Hawk

4.45

- 1 -

0.63

6.34

1.06

3.16

± 0.76

12.70

3.92

Roadside Hawk

3.25

0.62

3.59

0.76

5.18

± 0.81

5.41

0.80

Common

Black-collared Hawk

2.36

0.53

2.73

0.55“

0.52

± 0.21

0.66

0.20“

Snail Kite

3.00

0.94

0.93

0.35

0.73

± 0.22

0.23

0.09

American Kestrel

R/NAM

0.25

0.13

0.23

0.10“

2.21

± 0.76

2.37

0.57“

White-tailed Hawk

1.41

0.24

0.82

0.18

0.48

± 0.24

0.68

0.17

Uncommon

Aplomado Falcon

0.61

0.17

0.84

0.20

0.57

± 0.13

0.60

0.16

Great Black Hawk

0.84

0.30

1.21

0.37

0.59

± 0.19

0.43

0.18

White-tailed Kite

0.32

0.09

0.39

0.12

1.48

± 0.40

1.50

0.32

Crane Hawk

0.30

0.10

0.61

0.14

0.27

± 0.11

0.55

0.19

Laughing Falcon

0.23

-h

0.12

0.18

0.13

0.93

± 0.27

1.09

-4-

0.38

Osprey

NAM

0.93

0.2U

0.38

0.14

O'*

0.28

0.11

“Relative abundance class: Very common = 10-26% of zill individuals detected; Common = 3-5%, Uncommon = 1-2%.

*^ Status: R = resident species, NAM = North American migratory species, R/NAM = resident and North American migratory
population.

^ Means denoted by “d” differed (P < 0.0018) between regions for the wet season. Means denoted by “D” differed {P < 0.0018)
between regions for the dry season. All other comparisons were not significant (P > 0.0018).

December 2005

The Raptor Community of the Li^nos

425

Table 4. Rare species detected during raptor surveys for combined years in the wet (2000 and 2001) and the dry
season (2001 and 2002) in the Southwestern and Western Llanos of Venezuela.

Relative

Southwestern {N = 28)

Western {N

= 22)

Abundance

Class'^

Species

Status'’

Wet

Dry

Wet

Dry

Rare

King Vulture

Harris’s Hawk

Gray-lined Hawk

Zone-tailed Hawk

Slender-billed Kite

Bat Falcon

Plumbeous Kite

Hook-billed Kite

Long-winged Harrier

Common Black Hawk

Peregrine Falcon

NAM

Short-tailed Hawk

Grey-headed Kite

Pearl Kite

“Relative abundance class: Rare = <1% of all individuals detected.

’’ Status: R = nonmigratory populations, NAM = North American migratory population.

Regional and Seasonal Patterns. The Western
Llanos was characterized by higher levels of raptor
diversity. This region underwent a period of exten-
sive deforestation prior to 1825, followed by forest
regeneration through 1950, and another period of
deforestation by 1975 (Veillon 1976). Forest ex-
ploitation cycles, coupled with agricultural activity
and year-round water sources, have resulted in a
dynamic mosaic of forest, savanna, agricultural,
pasture, and early successional habitats that likely
account for the high raptor diversity in this region.

Overall, raptor communities in the Southwest-
ern and Western Llanos were similar. However,
varying vegetation cover types, large-scale flooding,
and the availability of year round water sources
during the dry season almost certainly influence
the raptor community. For example, Balgooyen
(1989) reported the American Kestrel preferred
the forest-agriculture mosaic habitats in the Llanos.
Our data indicated this pattern was pronounced in
the dry season, when American Kestrel numbers
increased in the Western Llanos, likely due to the
arrival of wintering North American migrants. Fur-
thermore, several examples of seasonal influences
are apparent in the Southwestern Llanos, where
flooding of savanna and gallery forest is extensive
in the wet season, but also where wetland com-
plexes persist throughout the year. The higher
numbers of the Black-collared Hawk in this region

during the dry season were likely explained by the
presence of year-round wetland complexes. Simi-
larly, the higher numbers of Osprey in the South-
western Llanos versus Western Llanos during the
wet season indicated that Osprey used both regions
during the dry season, but first-year birds spent the
wet season in the Southwestern Llanos, where
flooding was extensive. Therefore, the year-round
availability of wetland complexes and the extensive
inundation of savanna in the wet season likely ex-
plains why these aquatic-dependent species are
more abundant in this region.

Raptor Distribution. Our results on the relative
abundance and distribution of the 14 most com-
mon species in our study were consistent with pre-
vious findings. However, 4 of 14 less common spe-
cies were not expected to occur in the Llanos, or
there was little information on their distribution
and seasonal occurrence: Common Black Hawk (5
individuals). Pearl Fate (6), Plumbeous Kite (9),
and Short-tailed Hawk (5). The Pearl Kite was re-
ported as scarce or absent in the Llanos (Hilty
2003), but was detected in greater numbers than
many species considered uncommon residents. Al-
though the distribution of the Short-tailed Hawk
was previously unknown in the Llanos (Hilty 2003),
we detected this species in low numbers through-
out the study area. Our observation that the Plum-
beous Kite was absent during the wet season sug-

426

Jensen et al.

VoL. 39, No. 4

gests the Llanos population was similar to those of
Central America, Mexico, and Trinidad. All of
these raptors migrate southward in August and
September and return north to breed in February
and March (Ferguson-Lees and Christie 2001).

Conservation Implications. The rich raptor com-
munity of the Southwestern and Western Llanos is
comprised of wetland-dependent and upland-ter-
restrial species, both nonmigratory and migratory,
of which several appear seasonally nomadic and
may depend on both regions as they move in and
out in response to the wet and dry seasons. This
pattern suggests that, at least in part, the diverse
raptor community in the region owes its origins to
a combination of a large landscape with a substan-
tial seasonal influx of water and the forest-agricul-
tural mosaic that creates a temporally and spatially
diverse mix of habitats.

The Harris’s Hawk {Parabuteo unicinctus ) , Savan-
na Hawk, and White-tailed Hawk are now absent
from the Cauca Valley in Columbia as a result of
landscape homogenization and wetland depletion
(Alvarez-Lopez and Kattan 1995). We commonly
detected the Savanna Hawk and White-tailed
Hawk, and to a lesser extent the Harris’s Hawk,
throughout the Southwestern and Western Llanos,
which suggests large-scale landscape homogeniza-
tion and wetland degradation are not yet occurring
in these regions. In contrast, because hawk-eagles
may be less tolerant of human alterations on the
landscape than many other raptors (Burnham et
al. 1994), the Ornate Hawk-Eagle may have been
affected by historical deforestation and subsequent
lack of suitable habitats in these regions. However,
with the exception of the Ornate Hawk-Eagle, the
raptor community in the Llanos may represent a
community model for Neotropical savanna-forest-
agricultural regions.

Importantly, additional studies on the raptor
community in the Llanos are required to better
understand abundance patterns and seasonal fluc-
tuations of raptors. Eurthermore, research is need-
ed to evaluate local areas where deforestation, in-
tensive agriculture, and man-made impoundments
are currently expanding, which may be useful for
assessing the long-term stability of the current rap-
tor community. Finally, comparisons between the
Llanos and other Neotropical wetland-savanna
complexes, such as the Brazilian Pantanal, will help
determine the scope and representation of our
findings.

Acknowledgments

Duck’s Unlimited and the U.S. Department of Agri-
culture Forest Service provided the major financial sup-
port for this project, along with support from the Hawk
Mountain Sanctuary. Special thanks to our field assistants
Alexis Araujo, Mireya Barrera, David Peraza, Mariana Es-
cobar, Maria Doris Escovar, Andres DeGraf, Sara Seijas,
and Graciela Barrera and to the Universidad Nacional
Experimental de Los Llanos Occidentales Ezequiel Za-
mora (UNELLEZ) in Guanare for their collaboration
with the project and the generous use of their facilities.
Thanks to Don Taphorn, Jose Angel Anez of AsoMuseo,
Luis Altuve, Jose Gregorio Quintero, Gilberto Rios, An-
tonio Utrera, Andres Seijas, Franklin Rojas-Suarez of
Pro Vita, Alvaro Velasco from Profauna in Caracas, Jose
Gregorio Garcia Tenia and Yuri Cedeno from Profauna
in San Fernando, Richard Schargel and Heberto Pacheco
from BioCentro, Clemencia Rodner and Robin Restall
from the Audubon Society in Caracas, and Luis Gonzalez
Morales from the Universidad Central de Venezuela. Fi-
nally we gratefully thank the following landowners in the
Llanos for access to their properties and use of facilities,
the Maldonado family and staff members Alexis Aguirre,
Jose Ayarzaguena, and Sara Candela of Hato El Frio; Ing.
Jesus Pacheco and Enrique Loreto who authorized visits
to Hato El Cedral, where staff members Edgar Chiapan-
na and Ing. Tulio Aquilera provided assistance; the Bran-
ger family at Hato Pinero, where Edgar Useche autho-
rized visits; staff at Hato Fernando Corrales; and Don
Porfirio Martinez from Mantecal. This is Hawk Mountain
Sanctuary contribution to conservation science number
119.

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Received 27 May 2004; accepted 15 August 2005

J. Raptor Res. 39(4):429-438
© 2005 The Raptor Research Foundation, Inc.

A COMPARISON OF BREEDING SEASON FOOD HABITS OF
BURROWING OWLS NESTING IN AGRICULTURAL AND
NONAGRICULTURAL HABITAT IN IDAHO

Colleen E. Moulton,^ Ryan S. Brady, and James R. Belthoff

Department of Biology and Raptor Research Center, Boise State University, Boise, ID 83725 U.S.A.

Abstract. Through analysis of regurgitated pellets and prey remains collected at nests between 2001-

02, we characterized diet composition of western Burrowing Owls {Athene cunicularia hypugaea) in the
Snake River Birds of Prey National Conservation Area (NCA) of southwestern Idaho. We hypothesized
that diet differs between owls nesting in agricultural and nonagricultural habitat, because at least one
important prey species, montane voles (Microtus montanus), occurs predominately in the former. From
859 pellets, we identified 7402 prey items representing 23 species, and identified 403 prey remains of
19 species. Invertebrates dominated the diet in numbers of prey, whereas rodents contributed the great-
est biomass. Montane voles, which were not present in pellets in nonagricultural areas, represented the
greatest percent biomass of pellets in agricultural areas. Invertebrates (predominately Gryllidae) also
were more abundant in diets of owls nesting in agricultural habitat. Pellets of owls nesting in agricultural
areas had greater species richness, whereas pellets from nonagricultural areas had greater species even-
ness and broader food-niche breadths. Finally, we estimated food-niche breadth of Burrowing Owls in
the NCA to be broader than previously reported.

Key Words: Burrowing Owl; Athene cunicularia; agriculture; food habits; food-niche; Idaho.

UNA COMPARACION DE LOS hAbITOS ALIMENTICIOS DE INDIVIDUOS NIDIFICANTES DE
ATHENE CUNICULARIA EN AMBIENTES AGRICOLAS Y NO AGRICOLAS EN IDAHO

Resumen. — A traves del analisis de egagropilas y de restos de presas recolectados en nidos en 2001 y
2002, caracterizamos la composicion de la dieta de Athene cunicularia hypugaea en el Area Nacional de
Conservacion de Aves de Presa Snake River, sudoeste de Idaho. Nos planteamos la hipotesis de que la
dieta difiere entre las lechuzas que nidifican en ambientes agricolas y no agricolas, debido a que al
menos una de las especies de presa importantes, Microtus montarius, se encuentra predominantemente
en las areas agricolas. De un total de 859 egagropilas, identificamos 7402 items de presas correspon-
dientes a 23 especies, e identificamos 403 restos de presas provenientes de 19 especies. Los invertebrados
dominaron la dieta en terminos del numero de presas, mientras que los roedores representaron la
mayor biomasa. Microtus montanus no estuvo presente en las egagropilas de las areas no agricolas y
represento el mayor porcentaje de biomasa en las egagropilas de las areas agricolas. Los invertebrados
(predominantemente Gryllidae) tambien fueron abundantes en las dietas de las lechuzas que nidifica-
ron en los ambientes agricolas. Las egagropilas de las lechuzas que nidificaron en las areas agricolas
presentaron mayor riqueza de especies, mientras que las provenientes de las areas no agricolas presen-
taron mayor equidad y nichos alimenticios mas amplios. Finalmente, estimamos que el nicho alimenticio
de A. c. hypugaea en el area silvestre de conservacion estudiada es mas amplio de lo que habia sido
informado previamente.

[Traduccion del equipo editorial]

Agricultural practices historically have provided
many different types of wildlife habitat, including
shelterbelts, hedgerows and fencerows, cultivated
fields, and fields in rotation. Although some spe-
cies nest, seek cover, and forage in these habitats,

1 Present address: Wildlife Bureau, Idaho Department of
Fish and Game, P.O. Box 25, Boise, ID 83707 U.S.A.;
email address: cmoulton@idfg.idaho.gov

many wildlife populations have declined signifi-
cantly in areas of agricultural conversion (Carlson
1985, Murphy 2003). In fact, there is mounting ev-
idence that converting natural landscapes into ag-
ricultural use can affect a wide array of wildlife
populations through erosion, exposure to herbi-
cides and pesticides, and destruction of nesting
and cover habitat (Carlson 1985, Jahn and Schenck
1991, Gervais et al. 2000). These effects may be

429

430

Moulton et al.

VoL. 39, No. 4

amplified by the shift from small-scale farming
practices to large-scale monoculture farming seen
throughout the United States and Canada (Peter-
john 2003).

Western Burrowing Owls {Athene cunicularia
hypugaea) are listed as Endangered in Canada and
several western U.S. states, and their populations
are declining in many areas (e.g., James and Espie
1997, Clayton and Schmutz 1999, Klute et al.
2003). These owls suffer deleterious effects from
agricultural practices (James and Fox 1987, Haug
et al. 1993, Bellocq 1997, Gervais et al. 2000) and,
in Canada, often avoid agricultural fields (Haug
and Oliphant 1990, Clayton and Schmutz 1999).
However, throughout some portions of their west-
ern U.S. range. Burrowing Owls associate with ag-
riculture (Rich 1986, DeSante et al. 2004, Moulton
et al., in press), and they are the only raptor spe-
cies that shows significant affinity for agriculture in
southern Idaho (Leptich 1994). Rich (1986) sug-
gested that proximity to montane voles {Microtus
montanus) in farmlands could explain some of this
habitat selection. Moulton et al. (in press) con-
firmed that owls did not nest in agricultural areas
because of decreased nest predation or increased
availability of nesting sites but noted that prey con-
sumption was greater in agricultural areas.

If Burrowing Owl nesting distributions can be
affected by prey, as Rich (1986) and Moulton et al.
(in press) hypothesize, then diet composition may
differ for owls occupying agricultural and nonag-
ricultural areas. Thus, the objective of our study
was to examine breeding season food habits of
Burrowing Owls in the Snake River Birds of Prey
National Conservation Area (NCA), where Burrow-
ing Owls inhabit both agricultural and nonagricul-
tural areas. Specifically, we tested the hypotheses
that (1) diets of owls in agricultural areas contain
more montane voles than those in nonagricultural
habitats and (2) because of influences of agricul-
tural practices, diet diversity and food-niche
breadths differ. We predicted that Burrowing Owls
nesting in agricultural habitats would have greater
prey diversity and broader food-niche breadths
than owls nesting in nonagricultural habitats. Fi-
nally, we compared our food-niche breadth esti-
mates with those of a previous study (Marti et al.
1993) on raptor food habits in the NCA.

Methods

We studied Burrowing Owls nesting within and near
the NCA in southwestern Idaho during 2001-02. This
area was once representative of a typical shrub-steppe
community dominated by large expanses of big sage-

brush {Artemesia tridentata xvyomingensis; Hironaka et al.
1983) and other shrubs, and scattered perennial bunch-
grasses. However, disturbances, such as range fires, mili-
tary training, grazing, and off-road vehicle use, have
helped convert much of the area to exotic annual grass-
lands dominated by cheatgrass {Bromus tectorum), tumble
mustard {Sisymbrium altissimum), and other non-native
species (Hironaka et al. 1983). Surrounding areas also
contained scattered residential homes, paved and dirt
roads, a military training area, and public lands managed
by the Bureau of Land Management. Cattle and sheep
graze much of the area, especially during winter. Irrigat-
ed agricultural fields (primarily alfalfa, sugar beets, and
mint) constituted <5% of the NCA and were located pri-
marily along its margins (USDI 1996). For the purpose
of this study, we considered Burrowing Owl nests that
were within 1 km of an irrigated agricultural field, to be
in “agricultural” habitat (hereafter agricultural nests).
Agricultural nests were located in the natural vegetation
surrounding agriculture fields rather than in the irrigat-
ed portions where crops grew. However, adult owls fre-
quently hunted within these fields and perched on fence
posts adjacent to them (Moulton et al. in press). “Non-
agricultural” habitat was the term we used to categorize
nests that were greater than 3 km from irrigated fields
(hereafter nonagricultural nests). Because this distance
exceeded the typical foraging range of Burrowing Owls
(Haug and Oliphant 1990, Rosenberg and Haley 2004),
we are almost certain that owls from nonagricultural
nests were not collecting prey from or near irrigated
fields. Nonagricultural areas were generally disturbed
shrublands and grasslands much like that in the agricul-
tural areas, but there were no crops or irrigation nearby

Diet Composition. Regurgitated pellets are reliable in-
dicators of the diet of Burrowing Owls (Marti 1974), al-
though amphibians and reptiles can be underrepresent-
ed in pellets (Thomsen 1971, Haug 1985). Similarly, prey
remains alone do not provide reliable information re-
garding overall diet composition, as many prey items con-
sumed by Burrowing Owls are too small to cache (such
as small insects) . But, remains provide better information
than pellets concerning amphibians and reptiles in the
diet. Therefore, to determine diet composition, we both
documented prey remains at nests and collected and an-
alyzed regurgitated pellets.

Pellet Collection and Analysis. We collected regurgitat-
ed pellets from tunnel entrances, perches, and nearby
mounds within 20 m of nest burrows every 3-10 d from
hatching through 25 d post-hatch (May-June) . For nests
at which we collected more than 20 pellets (29 of 51
nests; 22 agricultural, 7 nonagricultural), we analyzed a
random sample of 20 pellets per nest. For all other nests,
we analyzed all collected pellets (11.2 — 1.0 [SE] pellets
per nest, range = 4-19).

We analyzed and quantified remains of each pellet us-
ing standard procedures (Marti 1987) and by comparing
prey species to a museum collection at Boise State Uni-
versity. Skulls, jaws, dentition patterns, head capsules,
pronota, elytra, legs, scales and other distinguishing body
parts helped identify prey.

Prey Remains. Owls in this study nested in artificial
burrows deployed for other studies (Smith and Belthoff
2001, Belthoff and Smith 2003, Brady 2004, Moulton et
al. in press), which provided access to nest chambers.

December 2005

Burrowing Owl Food Habits in Idaho

431

where we found most prey remains. We could therefore
document cached and uneaten prey remains at all oc-
cupied nests and adjacent satellite burrows (non-nest
burrows used by owls for roosting, cover, and caching
prey) . We quantified prey remains each time we excavat-
ed an artificial burrow (2-5 visits per nest) between
hatching and 25 d post-hatch.

Biomass Estimation. We determined biomass of rep-
resentative mammalian, avian, and amphibian prey using
Smith and Murphy (1973) and Steenhof (1983). Biomass
of invertebrate prey species was determined using our
own estimates obtained from captured live specimens
(Moulton 2003) and values reported in Smith and Mur-
phy (1973) and Olenick (1990).

Statistical Analysis. Because we obtained prey remains
from only two nonagricultural nests, we did not include
data from prey remains in diversity calculations described
below or in statistical comparisons; instead, pellet data
provided all information used for these calculations and
comparisons. We determined each prey type as a percent
of total prey items per nest (percent number) and per-
cent biomass per nest.

We determined food-niche breadth for agricultural
and nonagricultural nests by calculating the reciprocal of
Simpson’s index (Simpson 1949). We calculated dietary
evenness using the Alatalo (1981) modification of Hill’s
(1973) index: F = - l)/(Wi - 1).

To determine if differences in diets existed between
owls nesting in each habitat, we compared percent num-
ber and percent biomass of each prey taxa (vertebrates) ,
class (invertebrates), or order (invertebrates) per nest us-
ing Wilcoxon’s ranked sums tests (Zar 1999). If there
were differences between habitats in taxa/ order of prey,
we then compared species (vertebrates) or families (in-
vertebrates) of that taxa/order. Because we made multi-
ple comparisons of prey categories, we adjusted alpha lev-
els using sequential Bonferroni corrections (Rice 1989).

To determine if diet diversity differed between agri-
cultural and nonagricultural nests, we compared food-
niche breadth (Simpson’s index), species richness (num-
ber of species in the diet), and dietary evenness (Alatalo’s
index) using Wilcoxon’s ranked sums tests. Statistical
analyses were performed using JMPIN V.5 (SAS Institute,
Inc., Cary, NC), and evaluated at an alpha level of 0.05
unless otherwise noted. Throughout, we present means
with their standard errors.

Results

Pellet Remains. We analyzed 602 regurgitated
pellets from 34 agricultural nests and 257 pellets
from 19 nonagricultural nests. From these, we
identified 7402 prey items representing 23 differ-
ent prey species.

Overall pellet composition. Invertebrates were the
most frequent prey in pellets, representing 93% of
prey items; however, they represented only 23% of
biomass (Table 1). Conversely, vertebrates (ro-
dents, birds, and herpefofauna) comprised 7% of
prey items, but 77% of biomass.

Coleopterans (beetles) and Orthopterans (crick-
ets, grasshoppers) were the most common inver-

tebrates in pellets, constituting 47% and 32% of
total prey, respectively (Table 1 ) . Of Coleopterans,
ground beetles (Carabidae) and darkling beetles
(Tenebrionidae) were most common (33% and
22% of Coleopteran prey items, respectively). Or-
thopteran prey remains were predominately Grylli-
dae (crickets), which constituted 73% of Orthop-
teran prey items.

Rodents were the most common vertebrates in
pellets and represented 97% of vertebrates detect-
ed and 73% of overall prey biomass (Table 1).
Pocket mice {Perognathus parvus) and deer mice
(Peromyscus maniculatus) were the most abundant
rodents (37% and 25%, respectively), but montane
voles represented the greatest biomass (18%).

Habitat variation. Invertebrates were the most fre-
quent prey in pellets for both agricultural and non-
agricultural nests, representing 95% and 90% of
total prey items, respectively (Table 2). Vertebrate
prey (mostly rodents) represented the greatest per-
cent biomass in both agricultural (76%) and non-
agricultural (79%) nests.

Coleopterans were the most common inverte-
brates in both habitats (Table 2). However, Arach-
nids contributed the greatest biomass (52%) of
invertebrates in nonagricultural nests, and Orthop-
terans contributed the greatest biomass (52%) of
invertebrates in agricultural nests. Of rodent spe-
cies found in pellets, deer mice and pocket mice
were most common in agricultural and nonagri-
cultural nests, respectively. Pocket mice also con-
tributed the greatest biomass of rodents at nonag-
ricultural nests, but montane voles contributed the
greatest biomass of rodents at agricultural nests.
Only owls at agricultural nests preyed on montane
voles (Table 2).

Agricultural and nonagricultural nests did not
differ in percent biomass of vertebrates or inver-
tebrates (Table 3) . However, agricultural nests had
a greater percent number of invertebrates, and
nonagricultural nests had a greater percent num-
ber of vertebrates. Pellets from agricultural nests
had greater percent number and percent biomass
of montane voles (Table 4). Nonagricultural nests
had greater percent number and biomass of pock-
et mice (Table 4) . Among invertebrates. Arachnids
and Orthopterans differed between habitats (Table
3). Solpugida (windscorpions) and Acrididae oc-
curred in greater percent number and biomass in
pellets of nonagricultural nests, while Gryllidae oc-
curred in greater number and biomass in pellets
at agricultural nests (Table 5).

For all nests combined, food-niche breadth was

432

Moulton et al.

VoL. 39, No. 4

Table 1. Mean (±SE) percent number and percent biomass per nest of prey items detected in pellets collected at
53 Burrowing Owl nests in southwestern Idaho, 2001-02.

Prey Category

Percent Number

Percent Biomass

Mammals

6.7

“h

0.7

72.9

— b

2.5

Spermophilus mollis

0.2

0.1

10.2

-1-

3.4

Thomomys townsendii

0.2

0.1

12.4

3.5

Perognathus parvus

2.5

0.6

12.5

2.5

Dipodomys ordii

0.6

-h

0.2

9.4

2.4

Reithrodontomus megalotis

0.1

— K

0.1

0.3

0.1

Peromyscus maniculatus

1.7

“b

0.4

11.1

-b

2.5

Mus musculus

0.2

0.1

1.2

“b

0.5

Microtus montanus

0.9

0.2

13.2

-b

2.8

Rodent — unidentified^

0.4

“h

0.1

2.7

-b

0.7

Birds — unidentified^

0.2

H-

0.1

2.2

0.8

Reptiles and Amphibians'^

<0.1

-h

0.1

1.9

-b

1.2

Arachnids

13.8

-h

1.9

6.3

-b

1.0

Scorpionida

5.8

-h

1.0

3.5

-b

0.9

Solpugida

8.0

H-

1.5

2.8

-b

0.5

Orthopterans

31.6

-b

3.2

9.6

-b

1.6

Acrididae

2.9

-b

0.6

0.7

0.1

Gryllidae

23.2

-b

3.5

7.7

-b

1.7

Unknown Orthoptera

5.5

-b

0.9

1.2

-b

0.2

Dermapterans (Forficulidae)

0.4

-b

0.2

H-

0.1

Homopterans (Cicadidae)

0.1

-b

0.1

Coleopterans

47.0

-b

2.6

6.8

0.7

Carabidae

15.7

2.2

1.9

-b

0.3

Scarabidae

7.5

1.3

1.1

H-

0.2

Silphidae

8.0

1.4

1.1

H-

0.2

Tenebrionidae

10.6

-b

1.9

2.3

-H

0.4

Coleoptera — unidentified

5.3

1.2

0.5

0.1

Total vertebrates

6.9

H-

0.7

77.0

2.1

Total invertebrates

93.1

0.7

23.0

-b

2.1

^ Mouse species: likely P. parvus, R. megalotis, P. maniculatus, or M. musculus.

^ Likely Eremophila alpestris or Sturnella neglecta.

Includes Bufo woodhousei, Phrynosoma platyrhinos, and unknown snake species.

4.22 ± 0.22 {N = 53). Nonagricultural {N = 19)
nests had greater species evenness than agricultur-
al {N = 34) nests (0.76 ± 0.03 versus 0.60 ± 0.02;
Z = 3.89, P < 0.001) and broader food-niche
breadth (5.21 ± 0.33 versus 3.67 ± 0.25; Z = 3.24,
P — 0.001). However, agricultural nests had higher
species richness (11.82 ± 0.40 versus 9.79 ± 0.54;
Z = -2.69, P = 0.007).

Prey Remains. We recorded cached and other
uneaten prey remains at 43 nests {N = 41 agricul-
tural, N— 2 nonagricultural) and documented 403
prey items representing 19 species (Table 6). Be-
cause we had so few nonagricultural nests, we
made no comparisons between habitats and
pooled data from all nests for descriptions of prey
remains.

Although common in pellets, invertebrate prey
remains were uncommon in nest burrows {N = 50
individual invertebrate prey items) . The majority of
prey remains in both percent number (87.6%) and
percent biomass (99.7%) were vertebrates, most of
which were rodents. Of rodent species, montane
voles were most common by number (36%), and
pocket gophers represented the greatest biomass
(50%).

Although rare in pellets, we occasionally found
herpetofauna (N — 38) and birds {N = 18) cached
in burrows. Woodhouse’s toads {Bufo woodhousei)
were the most common (92%) herpetofauna in
nest burrows. All toads were in nests adjacent to
agricultural fields. Burrowing Owl nestlings were
the most common (50%) cached avian prey item

December 2005

Burrowing Owl Food Habits in Idaho

433

Table 2. Mean (±SE) percent number and percent biomass per nest of prey items detected in pellets of Burrowing
Owls nesting in agricultural (N = 34) and nonagricultural (N = 19) habitats of southwestern Idaho, 2001-02.

Agricultural Nonagricultural

Prey Percent No. Percent Biomass Percent No. Percent Biomass

Mammals

4.9

0.8

70.7

-h

3.1

10.1 ±

1.1

76.9 ± 4.1

Spermophilus mollis

0.1

-h

0.1

5.3

4.1

0.5 ±

0.2

0.2 ± 0.1

Thomomys townsendii

0.4

-H

0.1

1.9

4.1

—

Perognathus parvus

0.7

0.6

4.9

2.6

5.6 ±

0.8

26.0 ± 3.4

Dipodomys ordii

0.4

0.2

4.9

2.8

1.2 ±

0.3

17.5 ± 3.8

Peromyscus maniculatus

1.4

0.5

10.5

3.1

2.1 ±

0.7

12.3 ± 4.2

Mus musculus

0.2

0.1

1.9

0.6

—

Microtus montanus

1.4

-h

0.3

20.6

3.1

—

Birds — unidentified^

0.1

H-

0.1

2.3

1.0

0.3 ±

0.1

2.0 ± 1.3

Reptiles and Amphibians*’

0.1

-+-

0.1

2.8

1.5

0.1 ±

0.1

0.3 ± 2.0

Arachnida

6.7

1.7

3.7

1.1

26.5 ±

2.3

10.9 ± 1.4

Scorpionida

3.3

-h

1.1

2.0

1.0

10.3 ±

1.5

6.0 ± 1.4

Solpugida

3.4

H-

1.6

1.7

0.6

16.2 ±

2.1

4.9 ± 0.8

Orthoptera

40.0

3.5

12.7

1.9

16.7 ±

4.7

4.0 ± 2.6

Acrididae

1.8

-t-

0.8

0.5

H-

0.2

4.9 ±

1.0

1.1 ± 0.2

Gryllidae

34.8

3.5

11.4

-h

1.9

2.3 ±

4.7

1.0 ± 2.5

Coleoptera

47.6

3.2

7.5

0.8

46.1 ±

4.3

5.7 ± 0.1

Carabidae

21.4

-t-

2.4

2.7

0.4

5.5 ±

3.2

0.7 ± 0.5

Scarabidae

5.6

-h

1.5

1.0

0.3

10.9 ±

2.0

1.3 ± 0.4

Silphidae

5.1

1.7

0.9

0.3

13.2 ±

2.3

' 1.4 ± 0.4

Tenebrionidae

11.1

-h

2.3

2.5

H-

0.6

9.6 ±

3.1

1.9 ± 0.7

Total vertebrates

5.0

0.8

75.8

2.6

10.3 ±

1.1

79.1 ± 3.5

Total invertebrates

95.0

0.8

24.2

2.6

89.7 ±

1.1

20.9 ± 3.5

“ Likely Eremophila alpestris or Sturnella neglecta.

Includes Bufo woodhousei, Phrynosoma platyrhinos, and unknown snake species.

we found. These Burrowing Owl nestlings all were
individuals from nests other than the nest in which
we found them. Whether they wandered into the
nest on their own and subsequently starved or were
killed or were taken directly from their nest is un-
known. We suspect that adults tending nearby nests
preyed upon these nestlings because they frequent-
ly were too young to have wandered into nests oth-
er than their own.

Discussion

The NGA supports one of the highest densities
of breeding raptors in the world (Marti et al.
1993), and many previous studies have examined
food habits of nesting raptors there (e.g., Marks
and Marks 1981, Marks and Doremus 1988, Marti
1988, Steenhof and Kochert 1988). However, die-
tary habits and trophic relationships of Burrowing
Owls remain the least well-understood of raptors
breeding in the NCA (Marti pers. comm.). Thus,
our study filled an important knowledge gap in

raptor ecology within the NCA. Our study found:
(1) no one species dominated the vertebrate com-
ponent of Burrowing Owl diets, unlike owls in oth-
er regions; (2) diets differed by habitat, most no-
tably that montane voles and crickets were
important prey for agricultural nests, but they were
not part of the diet for nonagricultural nests; and
(3) the food-niche breadth of Burrowing Owls in
the NCA is broader than previously estimated.

Burrowing Owl Diet in the NCA. Burrowing
Owls are considered opportunistic predators
(Gleason and Craig 1979, Green et al. 1993, Haug
et al. 1993), and the wide variety of prey owls con-
sumed in our study area is consistent with this no-
tion. Similar to studies in Colorado (Marti 1974),
Saskatchewan (Haug 1985), and the Idaho Nation-
al Engineering Laboratory (INEEL) in Idaho
(Gleason and Craig 1979), invertebrates represent-
ed approximately 90-95% of prey items in regur-
gitated pellets, but they constituted only 20-30%
of biomass of prey. In contrast, Olenick (1990), in

434

Moulton et al.

VoL. 39, No. 4

Table 3. Mean (±SE) percent number and percent biomass per nest of vertebrate (taxa) and invertebrate (class/
order) prey detected in pellets of Burrowing Owls nesting in agricultural {N = 34) and nonagricultural {N = 19)
habitats of southwestern Idaho, 2001-02.

Habitat

Prey Category Agricultural Nonagricultural Z® P-value

Percent Number

Mammal

4.9

0.8

10.1

-h

1.1

3.01

0.003*

Bird

0.1

0.3

-h

0.1

0.22

0.823

Reptile and Amphibian

0.1

-h

0.1

-0.38

0.701

Arachnid

6.7

1.7

26.5

2.3

4.98

<0.001*

Orthopteran

40.0

3.5

16.7

4.7

-3.61

<0.001*

Goleopteran

47.6

3.2

46.1

4.3

-0.29

0.774

Total vertebrates

5.0

0.8

10.3

1.1

3.05

0.002*

Total invertebrates

95.0

0.8

89.7

1.1

-3.05

0.002*

Percent Biomass

Mammal

70.7

3.1

76.9

4.1

1.03

0.303

Bird

2.3

1.0

2.0

1.3

0.02

0.988

Reptile and Amphibian

2.8

1.5

0.3

2.0

-0.51

0.613

Arachnid

3.7

1.1

10.9

1.4

4.12

<0.001*

Orthopteran

12.7

1.9

4.0

-1-

2.6

-3.24

0.001*

Goleopteran

7.5

0.8

5.7

0.1

-0.99

0.321

Total vertebrates

75.8

-1-

2.6

79.1

-K

3.5

0.96

0.340

Total invertebrates

24.2

2.6

20.9

3.5

-0.96

0.340

® Data were compared using Wilcoxon’s ranked sums tests.

* Significant based on sequential Bonferroni corrections adjusted from an original alpha level of 0.05 for a total of 16 comparisons

Table 4. Mean (±SE) percent number and percent biomass per nest of rodent species detected in pellets of Bur-
rowing Owls nesting in agricultural {N = 34) and nonagricultural {N = 19) habitats of southwestern Idaho, 2001-02.

Habitat

Prey Species Agricultural Nonagricultural P-value

Percent Number

Spermophilus mollis

0.1

0.5

0.2

1.83

0.067

Thomomys townsendii

0.4

0.1

0.0

-h

0.1

-2.72

0.007

Perognathus parvus

0.7

-+-

0.6

5.6

0.8

4.23

<0.001*

Dipodomys ordii

0.4

-+-

0.2

1.2

-h

0.3

1.67

0.095

Peromyscus maniculatus

1.4

0.5

2.1

-1-

0.7

-1.43

0.153

Mus musculus

0.2

0.1

0.0

0.1

-2.25

0.025

Microtus montanus

1.4

0.3

0.0

0.4

-4.32

<0.001*

Percent Biomass

Spermophilus mollis

5.3

4.1

0.2

-h

0.1

1.86

0.063

Thomomys townsendii

1.9

H-

4.1

0.0

-1-

5.4

-2.72

0.007

Perognathus parvus

4.9

2.6

26.0

3.4

4.00

<0.001*

Dipodomys ordii

4.9

2.8

17.5

3.8

1.79

0.073

Peromyscus maniculatus

10.5

3.1

12.3

4.2

-1.05

0.294

Mus musculus

1.9

0.6

0.0

0.8

-2.25

0.025

Microtus montanus

20.6

3.1

0.0

4.2

-4.32

<0.001*

Data were compared using Wilcoxon’s ranked sums tests.

* Significant based on sequential Bonferroni corrections adjusted from an original alpha level of 0,05 for a total of 14 comparisons

December 2005

Burrowing Owl Food Habits in Idaho

435

Table 5. Mean (±SE) percent number and percent biomass per nest of Arachnid orders and Orthopteran families
detected in pellets of Burrowing Owls nesting in agricultural {N = 34) and nonagricultural {N = 19) habitats of
southwestern Idaho, 2001-02.

Prey Order/Family

Habitat

Agricultural

Non agricultural

P-VALUE

Percent Number
Arachnida
Scorpiones

3.3 ± 1.1

10.3 ± 1.5

2.22

0.026

Solpugida

3.4 ± 1.6

16.2 ± 2.1

4.04

<0.001*

Orthoptera

Acrididae

1.8 ± 0.8

4.9 ± 1.0

2.81

0.005*

Gryllidae

34.8 ± 3.5

2.3 ± 4.7

-5.43

<0.001*

Percent Biomass

Arachnida

Scorpiones

2.0 ± 1.0

6.0 ± 1.4

1.72

0.086

Solpugida

1.7 ± 0.6

4.9 ± 0.8

3.68

<0.001*

Orthoptera

Acrididae

0.5 ± 0.2

1.1 ± 0.2

2.38

0.017*

Gryllidae

11.4 ± 1.9

1.0 ± 2.5

-5.26

<0.001*

Data were compared using Wilcoxon’s ranked sums tests.

* Significant based on sequential Bonferroni corrections adjusted from an original alpha level of 0.05 for a total of four comparisons
each for Arachnida and Orthoptera.

southeastern Idaho, reported that invertebrates
represent only 60% of the number of prey items
and less than 3% of the biomass, and owls in the
Imperial Valley, California, feed almost exclusively
on invertebrates (York et al. 2002).

Although invertebrates generally constitute a
large percentage of prey Burrowing Owls consume,
the orders and families that are most common in
the diet vary among regions. For example, Cole-
opterans were the most abundant invertebrate spe-
cies in our study, as well as in Colorado (Marti
1974), Washington (Green et al. 1993), and
Oregon (Green et al. 1993), whereas Jerusalem
crickets (Stenopelmatus spp.) were the most impor-
tant invertebrate prey species, in terms of biomass,
for Burrowing Owls in Oregon (Green et al. 1993),
California (Thomsen 1971), and southeastern Ida-
ho (Gleason and Craig 1979).

Vertebrates accounted for most of the biomass
in our study, but no one vertebrate species domi-
nated the diet. Percent biomass of montane voles
(17%), pocket mice (16%), pocket gophers (16%),
and deer mice (14%) were similar. In contrast, Mi-
crotus sp. were the predominant vertebrate prey
item in Montana (Holt et al. 2001) and represent-
ed 80% of biomass in owl diets in southeastern Ida-

ho (Olenick 1990), and pocket mice dominated
rodent prey in Oregon (97%; Green 1983). This
lack of a dominant vertebrate prey may indicate a
diverse prey base in our study area (Moulton et al.
in press).

Agricultural versus Nonagricultural Nests. Com-
parisons of pellet remains from Burrowing Owl
nests in agricultural and nonagricultural areas re-
vealed different prey composition, species rich-
ness, species evenness, and food-niche breadth. Al-
though both habitats had similar biomass of
vertebrates, nonagricultural areas had greater
numbers of rodent prey. In contrast, owls nesting
adjacent to agricultural fields in southeastern Ida-
ho had a higher proportion of rodents in their diet
than those nesting in more natural areas (Gleason
1978). Agricultural nests had a higher proportion
of invertebrates than nonagricultural nests, which
resulted from the high numbers of crickets present
in pellets from agricultural nests. Crickets were
rare in pellets of owls nesting in nonagricultural
habitats. Moulton et al. (in press) reported greater
prey consumption by Burrowing Owls nesting near
agricultural fields in the NCA; this difference pri-
marily resulted from greater invertebrate prey in
agricultural habitats. While some have suggested

436

Moulton et ai..

VoL. 39, No. 4

Table 6. Percent number, percent biomass, and total number of cached and other uneaten prey remains docu-
mented at 43 Burrowing Owl nests in southwestern Idaho, 2001-02.

Prey Category

Percent No.

Percent Biomass

Total No.

Mammals

73.70

87.67

297

^Ivilagus nuttallii

0.25

1.03

Thomomys townsendii

10.91

44.73

Dipodomys ordii

11.41

13.01

Perognathus parvus

2.48

0.77

Mus musculus

2.98

1.17

Mouse species®

18.86

5.86

Microtus montanus

26.80

21.10

108

Birds

4.47

8.09

Eremophila alpestris

0.25

0.09

Sturnus vulgaris

0.74

1.22

Sturnella neglecta

0.50

0.41

Passerine sp,^

0.25

0.15

Athene cuniculana — juv.

2.23

4.16

A. cunicularia — adult

0.25

1.03

Raptor sp.'^

0.25

1.03

Amphibians

8.68

3.60

Bufo woodhousei

8.68

3.60

Reptiles

0.74

0.29

Pituophis catenifer

0.74

0.29

Scolopendromorpha

0.50

0.00

Arachnids

10.92

0.34

Scorpiones

10.67

0.33

Solpugida

0.25

0.01

Orthopterans

0.50

0.01

Acrididae

0.25

0.00

Gryllidae

0.25

0.00

Total vertebrates

87.59

99.65

353

Total invertebrates

12.41

0.35

Total

403

Likely P. parvus, R. megalotis, P. maniculatus, or M. musculus.
Likely Eremophila alpestris or Sturnella neglecta.

Small juvenile hawk or Prairie Falcon {Falco mexicanus) .

that Burrowing Owls associate with irrigated agri-
culture because of the high abundance of montane
voles (Gleason 1978, Rich 1986), presence of high
numbers of invertebrate prey in the diet of owls in
agricultural habitat may indicate an overlooked im-
portance of invertebrate prey to breeding Burrow-
ing Owls in these areas.

Agricultural nests also had greater species rich-
ness than nonagricultural nests. Common rodent
species in agricultural habitats, such as montane
voles, were not in pellets of nonagricultural nests
and likely were not available in that habitat type.
However, nonagricultural nests had greater species

evenness than agricultural nests. This greater spe-
cies evenness likely contributed to our finding that
diets of owls nesting in nonagricultural areas had
a broader food-niche (i.e., greater diversity), as
Simpson’s diversity index can be greatly influenced
by species evenness.

Narrower food-niche breadths of Burrowing
Owls nesting near agricultural fields may indicate
a more specialized diet. As MacArthur and Pianka
(1966) proposed, one expects a species to special-
ize when prey availability is high (i.e., a productive
environment), and thus search time is low. A spe-
cies will generalize in unproductive environments

December 2005

Burrowing Owl Food Habits in Idaho

437

where search times are high. Therefore, if owls in
agricultural areas exhibit more specialized diets
relative to owls in nonagricultural areas, we pro-
pose that owls nesting in agricultural areas are ex-
periencing greater prey availability. This is consis-
tent with suggestions by previous researchers
(Gleason 1978, Rich 1986, Moulton et al. in press)
that Burrowing Owls associate with agriculture be-
cause of increased prey. However, further research
is needed to determine if the narrower food-niche
breadth of owls in agricultural areas results from
greater prey availability, where owls can be selec-
tive, or lower prey diversity.

Food-niche Breadth of Burrowing Owls in the
NCA. Prior to our study. Burrowing Owls in the
NCA were thought to have a very narrow food-
niche breadth compared to other raptor species
breeding there. Marti et al. (1993) estimated food-
niche breadth of Burrowing Owls to be only 2.43,
which was the narrowest food-niche breadth of all
12 raptor species studied. In contrast, food-niche
breadth of Burrowing Owls in our study was 4.22
± 0.22, which ranks Burrowing Owls seventh in
terms of food-niche breadth (first being the broad-
est). This disparity may be explained in part by
smaller sample sizes in Marti et al. (1993) com-
bined with different levels of identification; that is,
the 1993 study identified invertebrate prey to or-
der, whereas we identified invertebrates to family
when possible. Because this difference in prey level
identification would only affect the food-niche
breadth estimates of a species whose diet has a
large invertebrate component, only Burrowing Owl
estimates likely would be affected.

Compared to other raptors breeding within the
NCA, our study estimated food-niche breadths of
Burrowing Owls to be similar to Golden Eagles
{Aquila chrysaetos; 4.07) and Long-eared Owls {Asio
otus; 4.79; Marti et al. 1993). However, Burrowing
Owl diet composition is more similar to American
Kestrels {Falco sparverius), which also frequently
prey on invertebrates (Marti et al. 1993). In fact,
Burrowing Owls and American Kestrels are the
only two raptor species in the NCA for which in-
vertebrate prey comprises >1% of the diet (in
terms of biomass: 23% and 5%, respectively).

Acknowitdgments

We thank T. Booms, K. Donohue, C. Eaton, J. Egbert,
G. Fairhurst, K. Hasselblad, S. Lysne, R. Medeck, J.
Rausch, J. Soules, M. Troxler, and J. Urbanic for assis-
tance with fieldwork. Financial and logistical support was
provided through an ERA STAR Fellowship to C. Moul-
ton, grants from the Bureau of Land Management and

Idaho Department of Fish and Game, and the Depart-
ment of Biology and Raptor Research Center at Boise
State University. J. Clark, J. Doremus, and J. Sullivan fa-
cilitated our work in the Snake River Birds of Prey Na-
tional Conservation Area, and M. Fuller, Director of the
Raptor Research Center, was helpful in numerous ways
Finally, we thank J. Bednarz, C.S. Houston, J. Munger, T.
Rich, and I. Robertson for helpful comments on previous
versions of our manuscript.

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Received 1 December 2003; accepted 3 July 2005

J Raptor Res. 39(4) :439-444
© 2005 The Raptor Research Foundation, Inc.

RED-TAILED HAWK DIETARY OVERLAP WITH NORTHERN
GOSHAWKS ON THE KAIBAB PLATEAU, ARIZONA

Angela E. Gatto^

Bureau of Land Management, Lake Havasu, 2610 Sweetwater Avenue, Lake Havasu City, AZ 86406 U.S.A.

Teryl G. Grubb

Rocky Mountain Research Station, 2500 South Pine Knoll Drive, Flagstaff, AZ 86001 U.S.A.

Carol L. Chambers

School of Forestry, College of Ecosystem Science and Management, Northern Arizona University, P.O. Box 15018,

Flagstaff, AZ 86001 U.S.A.

Abstract. — ^We determined food habits of Red-tailed Hawks {Buteo jamaicensis) for comparison with
published information for Northern Goshawks {Accipiter gentilis) to evaluate potential competition on
the Kaibab Plateau, Arizona. We collected prey remains and pellets from 42 Red-tailed Hawk nests at
the end of the nesting season between August-October 1998-2001, and opportunistically from below
nest trees during site visits, May-July 2000-01. We identified 478 prey items, including 17 mammal, 7
bird, and 2 reptile species. Prey species frequency did not vary among years (P = 0.3), across habitat
types (P = 0.8), or by collection technique (P = 0.4). Annual food niche breadth for Red-tailed Hawks
averaged 0.57. Published mean niche breadth for Northern Goshawks was 0.32, supporting that Red-
tailed Hawks were feeding generalists, while Northern Goshawks were more specialized. However, 48%
of Red-tailed Hawk diet on the Kaibab Plateau consisted of species comprising a major portion of the
documented diet of Northern Goshawks, including Nuttall’s cottontail {Sylvilagus nuttallii), golden-man-
tled ground squirrel {Spermophilus lateralis lateralis), rock squirrel (5. variegates grammurus) , and Northern
Elicker ( Colaptes auratus) . Because raptor communities with high dietary overlap and lack of prey par-
titioning show food-limited nesting success, greater agnonistic behavior, and territoriality, Red-tailed
Hawks could be negatively affecting Northern Goshawks on the Kaibab Plateau.

Key Words: Red-tailed Hawk, Buteo jamaicensis; Northern Goshawk, Accipiter gentilis; competition', diet,

food habits; food niche breadth; foraging.

SOBRELAPAMIENTO DE LA DIETA DE BUTEO fAMAICENSlSY ACCIPITER GPAP/L/SEN LAMESETA
DE KAIBAB, ARIZONA

Resumen. — Determinamos la dieta de Buteo jamaicensis en la planicie de Kaibab, Arizona y la compara-
mos con informacion publicada sobre Accipiter gentilis con la finalidad de evaluar la posible existencia
de competencia entre estas dos especies. Recolectamos restos de presas y egagropilas de 42 nidos de B.
jamaicensis al final de la temporada reproductiva entre agosto y octubre de 1998-2001, y de forma
oportunista debajo de arboles de anidacion durante visitas a la zona de estudio realizadas entre mayo
y julio de 2000 y 2001. Identificamos 478 tipos de presas, induyendo 17 especies de mamiferos, 7 de
aves y 2 de reptiles. La frecuencia de las especies de presa no vario entre anos (P = 0.3), tipos de
habitat (P = 0.8) y tecnicas de colecta (P = 0.4). La amplitud anual del nicho alimentario de B.
jamaicensis promedio 0.57. Registros publicados indican que la amplitud del nicho alimentario de A.
gentilis es 0.32, lo cual sugiere que B. jamaicensis es una especie generalista, mientras que A. gentilis es
mas especializada. Sin embargo, el 48% de la dieta de B. jamaicensis en la planicie de Kaibab consiste
de especies que forman la mayor parte de la dieta documentada para A. gentilis, entre las que se
encuentran Sylvilagus nuttallii, Spermophilus lateralis lateralis, S. variegates grammurus y Colaptes auratus.
Debido a que las comunidades de rapaces que presentan un alto grado de superposicion en su dieta y
en las que no hay reparticion de presas muestran un bajo exito de anidacion debido a falta de alimento,

^ Email address: angela_gatto@blm.gov

439

440

Gatto et ai..

VoL. 39, No. 4

un mayor comportamiento antagonico y mayor territorialidad, B. jamaicensis podria estar afectando
negativamente a A. gentilis en la planicie de Kaibab.

[Traduccion del equipo editorial]

Fire suppression, timber harvesting, and live-
stock grazing over the past 100 yr have caused
changes in southwestern forests, including those
on the Kaibab Plateau in northwestern Arizona
(e.g.. Weaver 1951, Cooper 1960, Covington and
Moore 1994). Decreasing the quality and quantity
of climax forest can favor habitat generalists (Carey
1984) such as Red-tailed Hawks {Buteo jamaicensis) ,
which may out compete species dependent on late
successional forests, such as Northern Goshawks
{Accipiter gentilis; Andersen et al. 2003). Creation of
259-ha buffer zones on the plateau by the Kaibab
National Forest, although maintaining the quality
of old-growth for nesting sites, does not ensure suf-
ficient quantity or quality of old-growth forest be-
yond these protected areas (Reynolds et al. 1992).
Red-tailed Hawks often nest in abandoned North-
ern Goshawk nests after timber harvesting (Crock-
er-Bedford 1990). Beyond old-growth-managed
buffer zones, open areas may favor the hunting
style, and thus, increase foraging habitat of Red-
tailed Hawks more than Northern Goshawks. Ex-
ploring the potential relationship between these
two species facilitates a better understanding of
how upper level avian predators have adjusted to
human-caused alterations in southwestern forest
ecosystems. Further, this understanding could aid
resource managers in maintaining a viable North-
ern Goshawk population on the Kaibab Plateau.

Competition occurs when use or defense of a
resource by one individual reduces the availability
of that resource to other individuals (Gill 1990).
Interspecific competition occurs when individuals
of coexisting species require a resource that is in
limited supply relative to their needs such that sur-
vival or reproduction of at least one species is de-
creased (Ricklefs and Schluter 1993). On the Kai-
bab Plateau, Red-tailed Hawks and Northern
Goshawks, based on their proximity and similar
habitat use, could be competing for nest sites, for-
aging areas, or prey, despite potential partitioning
resulting from morphological and behavioral dif-
ferences between species (Ballam 1984, Squires
and Reynolds 1997). In this study, we focused on
determining the diet of Red-tailed Hawks for com-
parison with published information on Northern
Goshawks to evaluate potential overlap. We hypoth-

esized that Red-tailed Hawks and Northern Gos-
hawks, because of their close proximity and use of
similar nesting and foraging habitat, could also be
using the same prey species, creating the potential
for competition.

Study Area

The Kaibab Plateau, on the North Rim of the Grand
Canyon, is located in northwestern Arizona within the
Kaibab National Forest. The plateau encompasses 2980
km^ above 1830 m elevation. Our study area was confined
to 1732 km^ above the 2075 m contour to be consistent
with concurrent long-term Northern Goshawk research
on the plateau (Reynolds et al. 1994). Goshawk and Red-
tailed Hawk nest sites are interspersed throughout this
study area. Vegetation on the plateau consists of ponde-
rosa pine {Finns ponderosa) forest between 2075-2500 m;
mixed-conifer forest (ponderosa pine, Douglas-fir [Pseu-
dotsuga menziesii], white fir [Abies concolor], blue spruce
[Picea pungens] , and quaking aspen [Populus tremuloides ^ )
between 2500-2650 m; and Engelmann spruce-subalpine
fir {Picea engelmannii-Abies lasiocarpa) forest between
2650-2800 m (Rasmussen 1941, White and Vankat 1993)

Methods

Prey Remains and Pellet Identification. We collected
prey remains and regurgitated pellets from all known oc-
cupied Red-tailed Hawk nests {N = 21, 24, 32, 11 for
1998-2001, respectively), from below and in the nest, at
the end of the nesting season, August-October 1998-
2001, and opportunistically during the nesting season,
May-Jnly 2000-01. Collections from each nest were sep-
arated by >3 d, and end-of-season samples were collected
>30 d after previous collections. We treated each collec-
tion of pellets and prey remains from an occupied nest
as one sample for that nest site. We assumed prey species
identified in each sample had been consumed since the
last sample and represented new prey.

To identify prey, we separated samples into bones/frag-
ments, feathers, and hair. Bones and feathers were iden-
tified to the lowest taxon possible, through comparison
with S. Bayard’s reference prey collection stored at the
Rocky Mountain Research Station, Fort Collins, CO. We
identified hairs using keys (Williams 1938, Stains 1958,
Moore et al. 1974) and by comparing hairs directly with
samples from the Northern Arizona University, Depart-
ment of Biological Sciences’ collection and the private
collection of H.E. Graham (Flagstaff, AZ U.S.A.). The
characteristics we considered included color banding,
shape, presence of a hair shield, and configuration of a
medulla if present (Moore et al. 1974).

Determining diet via indirect means requires cautious
interpretation because of inherent biases associated with
each method (Lewis et al. 2004); however, identification
of a prey species in pellets and prey remains is an abso-
lute indication of presence. Therefore, we recorded one
occurrence whenever a species was found in a sample.

December 2005

Red-tailed Hawk Diet

441

We then pooled samples across years for each nest and
summed the number of times a prey species occurred.
This provided a conservative estimate of the relative im-
portance of prey species consumed by Red-tailed Hawks
at each nest. We also calculated the total number and
percent of nests at which each prey species occurred.

Prey Species Dissimilarity. Dyer (1978) developed a lin-
ear statistical analysis for comparing species dissimilarity
that can be used in conjunction with any species dissim-
ilarity index and is designed for data sets that involve
both multiple species and multiple environmental vari-
ables. Total species dissimilarity is divided into compo-
nents with one component being assigned to each envi-
ronmental variable or interaction of environmental
variables:

= Po + + W' + - +

where D^yis the (dis) similarity between observations zand
j, 5,yh) is a known function of i and j which corresponds
to the environmental variable or interaction, Pj is an
unknown parameter which represents the contribution
of the environmental variable or interaction to the
total dissimilarity, and cij is an error term with an ex-
pected value of 0.

We used this linear model with the Jaccard dissimilarity
index (Krebs 1998) to estimate whether the species iden-
tified in prey remains and pellets of Red-tailed Hawks
varied among years (1998-2001), vegetation types (pon-
derosa pine only, mixed conifer with pine dominant, or
mixed conifer only), or collection techniques (end of
season samples from nest or opportunistic samples col-
lected from below nest trees during nesting season). Jac-
card’s index is specifically designed for presence-absence
data, and because, by definition, rare species are typically
absent, rare species have little influence on the value of
the index (Krebs 1998). The Jaccard dissimilarity index
(D^J) is calculated by:

Djy = a/ {a + b + c)

where a is the number of binary characteristics present
m sample i and sample j, b is the number present only
in i, and c is the number present only in j. We estimated
Dyer’s model using the Jaccard index. We used permu-
tation methods (Edington 1995) to estimate a signifi-
cance level (P-value) for each environmental variable.
Statistical tests were significant if P < 0.05.

Niche Breadth. Niche breadth and niche overlap are
widely applied to analysis of foraging and community
ecology to estimate competition (Greene and Jaksic
1983). Niche breadths were calculated according to Lev-
ins’ (1968) equation:

P = for i = \ to n

Zj Pi^

where pi is the proportion of Red-tailed Hawk nests with
the taxon present. The value of p varies from 1 to n,
where n is the number of taxa. If prey taxa occur equally
among all nests, then p = ra. Niche-breadth values were
standardized and converted to a fraction ranging from 0
to 1 by the equation:

Pstandard = (P “ ^) / {n ~ 1).

To calculate niche breadth, we created a prey species

list based on pooled prey species present across all oc-
cupied Red-tailed Hawk nests by year. This yielded a sep-
arate food niche breadth measure for each of the four
study years. We also calculated a 95% confidence interval
for Red-tailed Hawk niche breadth on the Kaibab Plateau
for comparison with calculated niche breadths for North-
ern Goshawks from other studies.

Resuits

Pellet and Prey Remain Analysis. Considering
each visit’s collection of pellets and prey remains
as one discreet sample, we obtained 140 prey sam-
ples {N — 80 end of nesting season, 1998-2001; N
= 60 opportunistic during nesting season, 2000-

01) , consisting of 1-10 collections from 42 nests {x
= 3.3). We identified 478 prey items, including at
least 17 mammal, seven bird, and two reptile spe-
cies (Table 1). The number of species at any one
nest site ranged from 1-6. For all 4 yr combined,
mammals represented 72% of Red-tailed Hawk
diet and birds represented 27% (Table 1). Only
two reptile species were identified; they did not
contribute greatly to the overall diet (<1%). Six
species accounted for 67% of prey by frequency of
occurrence: Nuttall’s cottontail {Sylvilagus nuttallu,
17.6%), Kaibab squirrel (Sciurus aberti kaibabensis,
7.7%), rock squirrel {Spermophilus variegatus gram-
murus, 10.0%), golden-mantled ground squirrel {S.
lateralis lateralis, 10.3%), Northern Flicker {Colaptes
auratus, 10.7%), and Steller’sJay {Cyanocitta stellen,
10.3%; Table 1). Rare occurrences of porcupine
(Erethizon dorsatum) , coyote ( Canis latrans) , and
mule deer {Odocoileus hemionus) comprised <2% of
overall Red-tailed Hawk diet.

Dissimilarity Measures and Niche Breadth. Prey
species frequency identified from pellet and prey
remains did not vary among years {P = 0.3), across
habitat types {P = 0.8), or by collection technique
(P = 0.4). Dietary niche breadth for Red-tailed
Hawks pooled across nests for each year was 0.58
in 1998, 0.52 in 1999, 0.51 in 2000, and 0.65 in
2001. The mean and 95% confidence interval for
Red-tailed Hawks niche breadth for all four years
combined was 0.57 ± 0.11, Calculated food niche
breadths for Northern Goshawks for Arizona and
several other western states did not fall within our
confidence interval for Red-tailed Hawks (Table

2) . Dietary overlap between the Red-tailed Hawk
during this study and a Northern Goshawk diet
from BoaPs (1993) earlier study in the same area
was 55% (number of common species/sum of spe-
cies recorded for both raptors).

442

Gatto et al.

VoL. 39, No. 4

Table 1. Frequency of prey species in 140 samples (478 identified prey items) of pellets and prey remains collected
from 42 Red-tailed Hawk nests, May-October 1998-2001, on the Kaibab Plateau, Arizona, U.S.A.

Prey Species

Frequency
(N = 478)

Percent

Frequency

Nest

Occurrence
{N = 42)

Percent

Nest

Occurrence

Nuttall’s cottontail
{Sylvilagus nuttallii)

17.6

85.7

Golden-mantled ground squirrel
{Spermophilus lateralis)

10.3

61.9

Rock squirrel

{Spermophilus variegatus grammurus)

10.0

69.0

Kaibab squirrel

{Sciurus aberti kaibabensis)

7.7

50.0

Chipmunk
{Eutamias sp.)

5.6

47.6

Northern pocket gopher
{Thomomys talpoides)

4.6

50.0

Long-tailed vole

{Microtus longicaudus)

3.6

40.5

Red squirrel

( Tamiasciurus hudsonicus)

3.1

31.0

Mouse

{Peromyscus sp.)

2.7

21.4

Shrew
{Sorex sp.)

2.3

23.8

Black-tailed jackrabbit
{Lepus californicus)

1.7

19.0

Long-tailed weasel

{Mustela frenata arizonenst)

1.0

11.9

Mule deer

(Odocoileus hemionus)

1.0

11.9

Plains pocket mouse
{Perognathus flavescens)

0.6

4.8

Porcupine

{Erethizon dorsatum)

0.4

4.8

Ringtail

{Bassariscus astutus)

0.2

2.4

Coyote

{Canis latrans)

0.2

2.4

Northern Flicker
{Colaptes auratus)

10.7

66.7

Steller’s Jay

( Cyanocitta stelleri)

10.3

61.9

Clark’s Nutcracker
{Nucifraga Columbiana)

2.7

23.8

Unknown bird

1.7

16.7

Common Raven
{Corvus corax)

0.6

7.1

Western Bluebird
(Sialia mexicana)

0.2

2.4

Hairy Woodpecker
{Picoides villosus)

0.2

2.4

Common Nighthawk
( Chordeiles minor)

0.2

2.4

Unknown snake

0.6

4.8

Mountain short horned lizard^
{Phrynosoma douglassi)

0.0

^ Mountain short horned lizard was positively identified as a prey species during observations, but was not found in the prey collec-
tions.

December 2005

Red-tailed Hawk Diet

443

Table 2. Food niche breadth of nesting Northern Goshawks calculated from prey remains collected in Arizona and
other western states.

Location

Number of
Nests

Food Niche
Breadth

Source

Arizona

0.29

Boal and Mannan (1994)

California

114

0.41

Bloom et al. (1986)

New Mexico

0.36

Kennedy (1991)

Oregon

0.38

Reynolds and Meslow (1984)

Discussion

Our results on the Kaibab Plateau were consis-
tent with Red-tailed Hawks being feeding general-
ists and preying primarily upon rabbits {Sylvilagus
spp.), black-tailed jackrabbits {Lepus californicus) ,
and ground squirrels {Spermophilus spp; Preston
and Beane 1993); however, Northern Flickers and
Steller’s Jays were also frequent in this diet analysis.
Previous observation and prey remains analyses for
Northern Goshawks on the plateau indicated gos-
hawks also preyed mostly upon rabbits and hares,
tree and ground squirrels. Northern Flickers, and
Steller’s Jays (Boal and Mannan 1994, Kaufmann
et al. 1994, and Reynolds et al. 1994). Bosakowski
and Smith (1992) found that in eastern forests,
competition between accipiters and buteos is usu-
ally minimized by a difference in prey selection,
with buteos typically having a higher proportion of
mammals in their diet, and accipiters more avian
prey.

Red-tailed Hawks frequently exhibit switching
behavior, which is the capability to utilize which-
ever species is most abundant at the time (Steen-
hof and Kochert 1988). Predators that are gener-
alists often have weak and variable prey
preferences and will exhibit switching behavior,
while specialists with strong or consistent prefer-
ences do not (Murdoch 1969). The wider niche
breadth of Red-tailed Hawks on the Kaibab Plateau
indicated weaker preferences compared to the nar-
rower niche breadth of Northern Goshawks.

Red-tailed Hawks and Northern Goshawks fre-
quently occupy similar nesting habitat on the Kai-
bab Plateau. Both species tend to nest in larger
trees (x DBH = 68.3-72.5 cm) and mid-slope in
drainages (x slope position = 0.36-0.37; LaSorte et
al. 2004) . Because they also nest in close proximity
(<2000 m apart, USDA Forest Service, North Kai-
bab Ranger District unpubl. data), we suggest that
they may also be utilizing the same foraging habi-
tat. Unfortunately, pellets and prey remains do not

provide insight into any spatial or temporal parti-
tioning of prey by these two species. However, our
research clearly shows Red-tailed Hawks are prey-
ing upon many of the same species utilized by
Northern Goshawks. Thus, we believe the potential
for competition exists. We further hypothesize that
the more generalist nature of Red-tailed Hawk diet
and nesting habitat, in combination with the de-
terioration of late-successional forest habitat and
concurrent creation of openings on the Kaibab
Plateau, may tend to exacerbate any potential con-
flict. We suggest that additional research should be
implemented to examine this potential competi-
tion, better quantify numbers of prey in both spe-
cies’ diets, and determine potential effects on such
competition on Northern Goshawk management
alternatives.

Acknowledgments

We thank R. Reynolds for first conceiving of this pro-
ject; he, S. Bayard de Volo, S. Salafsky, and his summer
crews on the Kaibab Plateau provided field and logistical
support. A. Hales, R. Lopez, and T. Rohmer assisted with
data collection. R. Baida and P. Beier offered helpful
comments on study design, as well as the original man-
uscript. R. King provided invaluable statistical assistance.
We also thank D. Andersen and S. Lewis for thorough
and constructive reviews of the manuscript. This research
was part of the senior author’s Master of Science project
at Northern Arizona University, funded by U.S. Depart-
ment of Agriculture Forest Service, Rocky Mountain Re-
search Station.

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Received 15 March 2004; accepted 26 March 2005

Associate Editor: Clint W. Boal

BAT PREDATION BY LONG-EARED OWLS IN MEDITERRANEAN
AND TEMPERATE REGIONS OF SOUTHERN EUROPE

Ana Maria Garcia^

IMEDEA (CSIC-UJB), Miquel Marques 21, E-07190 Esporles, Mallorca, Spain

Francisco Cervera

C.R.F. Granja de El Saler, Conselleria de Territori i Habitatge, Avda. dels Pinars 106, E-46012, Valencia, Spain

Alejandro Rodriguez

Department of Applied Biology, Estadon Bioldgica de Donana, CSIC, Avda. Maria Luisa s/n, E-41013, Sevilla, Spain

Abstract. — ^We described spatial and temporal variation in bat consumption by Long-eared Owls {Asio
otus) at a coastal site of eastern Spain and examined the importance of bats in the diet of this raptor
in nine temperate and 21 Mediterranean localities of southern Europe. In our study site in Spain, bats
accounted for 2% of prey items, which is the largest percentage so far reported for the species. The
vast majority of bats were Pipistrellus spp. Bat predation occurred in all seasons, but was significantly
higher in spring and summer. The temporal pattern of bat predation was unrelated to temporal variation
in the consumption of rodents, the dominant prey in the diet. Although a consistent increase in bat
intake only in years of rodent scarcity predicts an aggregation of occurrences over time, bat occurrence
during 31 successive seasons was not different from a random sequence. Pellets containing bat remains
originated mainly from one communal roosting site. Bat remains appeared in pellets from five of 16
nests, accounting for 17% of prey items on average. In southern Europe, bats occurred in 38% of diets
in the Mediterranean region, while they were absent in diets from adjacent temperate localities. Our
results suggest that Long-eared Owls prey on bats rarely and opportunistically in Mediterranean sites,
but also that bat aggregations could be a locally important food source for some individual owls during
certain periods.

Key Words: Long-eared Owl, Asio otus; Chiroptera; diet, Mediterranean basin; trophic plasticity.

PREDACION de MURCIELAGOS POR el BUHO CHICO EN REGIONES TEMPLADAS YMEDITER-
rAneas del sur de EUROPA

Resumen. — Describimos la variacion espacial y temporal en el consumo de murcielagos por parte del
buho Chico Asio otus en una localidad costera del este de Espana, y examinamos la importancia de los
quiropteros en la dieta de esta rapaz en 30 local! dades del sur de Europa, 9 de clima templado y 21 de
clima mediterraneo. En nuestra area de estudio, los quiropteros constituyeron el 2% de las presas
ingeridas, cifra que representa el mayor consumo conocido para la especie. Casi todos los murcielagos
consumidos fueron a Pipistrellus spp. Su predacion se produjo en todas las estaciones, pero fue signifi-
cativamente mas alta en primavera y verano. El patron temporal de predacion de murcielagos no estuvo
relacionado con la variacion temporal en el consumo de roedores, la presa dominante en la dieta. El
incremento en el consumo de murcielagos solo en anos en los que los roedores son escasos predice
una agregacion temporal de las apariciones. Sin embargo, la presencia de murcielagos en la dieta a lo
largo de 31 estaciones sucesivas no difirio de una secuencia aleatoria. La mayor parte de las egagropilas
que contuvieron murcielagos procedieron del dormidero comunal. Encontramos restos de quiropteros
en cinco de los 16 nidos muestreados, donde constituyeron en promedio el 17% de las presas. En
Europa meridional, los murcielagos aparecieron en el 38% de las dietas de la region mediterranea,
pero en ninguna de las dietas de la region templada adyacente. Nuestros resultados indican que A. otus
consume murcielagos con baja frecuenda de forma oportupista en la region mediterranea, pero
tambien sugieren que las agrtipaciohes de quiropteros pueden ser una fuente de alimento localmente
importante para algunos individuos durante periodos concretos.

[Traduccion del autor]

^ Email address: panamel@ono.com

445

446

Garcia et al.

VoL. 39, No. 4

Throughout the boreal and temperate regions
of Europe, Long-eared Owls {Asio otus) prey almost
exclusively upon microtine rodents (Herrera and
Hiraldo 1976, Lundberg 1979, Marks et al. 1999).
As a result, owl numbers decrease locally with de-
clining vole (Microtus spp.) populations and, at
larger spatial scales, owls may use nomadic or ir-
ruptive movements to track peaks in vole abun-
dance (Lundberg 1979, Korpimaki 1985, Hanski et
al. 1991). Such a numerical response is a trait of
specialist predators that may be explained in part
by low availability of alternative prey (Weber et al.
2002) and by high predictability of vole population
peaks in such ecosystems (Korpimaki 1985). How-
ever, Long-eared Owls seem to depend less on ro-
dents at lower latitudes (Bertolino et al. 2001), es-
pecially in Mediterranean regions (Garcia and
Cervera 2001) which feature lower environmental
predictability, resulting in strong seasonal and an-
nual fluctuations in the abundance of rodents and
other prey (Blondel and Aronson 1999). Indeed
diet diversification with decreasing latitude may be
a general pattern in nocturnal raptors (Herrera
and Hiraldo 1976, Mikkola 1983, Korpimaki and
Marti 1995) and other predators (Revilla and Pa-
lomares 2002, Clavero et al. 2003) , suggesting that
specialization may not always reflect species-specif-
ic constraints in physiology or morphology, but be-
havioral flexibility (Futuyma and Moreno 1988,
Martin et al. 1995).

Bats have regularly been reported, albeit in small
amounts, as prey of a variety of diurnal and noc-
turnal raptors (e.g., Baker 1962, Ruprecht 1979,
Barclay et al. 1982). Long-eared Owls are no ex-
ception. For example, in the British Isles, this spe-
cies was the second most important bat predator
among raptors (Speakman 1991). In this paper, we
describe the pattern of bat consumption by Long-
eared Owls during an 8-yr period in a Mediterra-
nean site with good habitat for bats in terms of
roost (buildings) and food availability (insects in
rice fields and other flooded areas) . We also review
European studies of Long-eared Owl diet in the
Mediterranean basin and the adjacent temperate
zone to examine the geographical pattern of pre-
dation on bats. We predicted that occurrence of
bats in the Mediterranean sites would be higher
than in temperate sites of similar latitude because
(1) rodent abundance undergoes pronounced sea-
sonal and annual fluctuations, and owls must
search for alternative prey and (2) the season of
bat activity is longer, and bat average abundance

higher, in warmer Mediterranean environments
(Avery 1985, Altringham 1996).

Methods

We studied food habits of Long-eared Owls in Devesa
de I’Albufera, one Mediterranean coastal site near Valen-
cia city, Spain (39°21'N, 0°19'W). The owl habitat is a
mosaic of pine forest (Pinus halepensis) with dense un-
derstory and open areas, mostly dunes and mesic inter-
dune depressions (Costa et al. 1982). This forested land-
scape is highly disturbed (many buildings and regular
recreational activities) and surrounded by a large ex-
panse of rice fields. From November 1995 to June 2003,
we collected owl pellets from beneath roost and nest sites
on a monthly basis. We identified prey remains and, for
each pellet, determined occurrence and minimum num-
ber of individuals of prey species. Using these data, we
analyzed spatio-temporal fluctuations in bat predation.
For analysis of seasonal variation in bat consumption, sea-
sons were defined as winter ( January-March) , spring
(April-June) , summer ( July-September) , and fall (Oc-
tober-December) .

We carried out the biogeographic comparison of bat
predation using data from 30 diet studies from southern
Europe (Table 1). Each study area was assigned to the
Mediterranean or the temperate climate region accord-
ing to Emberger et al. (1963; Fig. 1). We excluded north-
ern temperate localities to avoid diets almost completely
dominated by voles. For diets containing bats, we used
Spearman correlation analysis to test the hypothesis that
proportion of bats decreased with increasing latitude and
altitude.

Results and Discussion

Bat Consumption in Devesa de I’Albufera, Coast-
al Spain. We collected 2012 pellets that contained
6210 prey items. Pellets containing bat remains
originated mainly from a communal roosting site
(60%) and also near 16 nest sites, where we re-
corded successful owl reproduction. Bats account-
ed for 2% of prey items (Table 1), which is the
largest percentage thus far reported for Long-
eared Owls (Marti 1976, Mikkola 1983; Table 1).
Of 126 bats, 124 were pipistrelle bats {Pipistrellus
spp; Table 2) . Bat remains occurred in all seasons,
but predation on bats was significantly higher dur-
ing the peak of bat activity and abundance in
spring and summer (G = 47.3, df = 3, P < 0.001;
Fig. 2) . In our study area, the first flights of young
pipistrelle bats take place between mid-July and
mid-August (D. Almenar and M. Monsalve pers.
comm.), and during the initial 2 wk their flight
skills are less than those of adults (Blanco 1998).
Thus, the combination of the annual peak in abun-
dance associated with the emergence of young bats
and their relatively higher vulnerability, associated
with their reduced flight capability, may help to

December 2005

Bat Predation by Long-eared Owls

447

Table 1. Long-eared Owl diet composition in 30 localities of southern Europe. Each locality is assigned to a climatic
region either Mediterranean or temperate. The percentage of bats, rodents, and other prey are calculated on the
total number of prey individuals. Numbers assigned to each study area are the same as in Fig. 1.

Study

Country

Climatic

Region^*

No. OF
Prey

Percent

Bats

Percent

Rodents

Percent

Other

Prey

Source

Spain

874

0.00

86.61

13.26

Alegre et al. 1989

Spain

232

0.00

96.10

3.90

Delibes et al. 1984

Spain

6929

0.04

90.70

9.20

Araujo et al. 1974

Spain

3726

0.00

92.60

7.30

San Segundo 1988

Spain

3185

0.03

78.50

21.50

Veiga 1980

Spain

255

0.00

96.50

2.80

Lopez-Gordo et al. 1977

Spain

804

0.00

72.60

27.40

Amat and Soriguer 1981

Spain

6210

2.03

52.77

45.20

This study

Spain

6249

0.08

89.00

10.70

Corral et al. 1979

France

368

0.00

58.40

39.13

Kayser and Sadoul 1996

Italy

494

0.00

90.08

9.72

Gerdol and Perco 1977

Italy

121

0.00

95.87

4.13

Gerdol and Perco 1977

Italy

103

0.00

54.37

45.63

Gerdol et al. 1982

Italy

1157

0.00

93.52

6.49

Casini and Magnani 1988

Italy

181

0.00

97.24

2.76

Capizzi et al. 1998

Italy

338

0.30

98.20

1.50

Plini 1986

Italy

1787

0.00

81.60

18.50

Guidoni et al. 1999

Italy

201

0.00

95.10

5.00

Capizzi and Luiselli 1996

Italy

—

0.11

70.70

28.40

Sublimi and Scalera 1991

Italy

234

<1.40

93.60

5.00

Sara 1990

Greece

961

0.30

87.90

11.70

Alivizatos and Goutner 1999

Italy

1787

0.00

81.60

18.40

Bertolino et al. 2001

Italy

1836

0.00

85.52

14.44

Galeotti and Can ova 1994

Italy

519

0.00

83.63

16.37

Mezzavilla 1993

Italy

655

0.00

93.44

6.56

Malavasi 1995

Italy

593

0.00

90.58

9.42

Aloise and Scaravelli 1995

Italy

0.00

79.59

20.40

Riga and Capizzi 1999

Slovenia

10991

0.00

95.48

4.52

Tome 2003a

Romania

1268

0.00

88.18

11.82

Marariu et al. 1991

Switzerland

4639

0.00

99.23

0.77

Roulin 1996

M = Mediterranean and T = temperate region.

explain the high occurrence of bats in summer
samples. The relative importance of bats in the diet
varied by year (G = 79.3, df = 6, P < 0.001; Fig.
2) . In our study area and other Mediterranean en-
vironments, rodent populations typically show an-
nual minima during summer, especially during
warm years (Blondel and Aronson 1999) . Although
owl consumption of rodents roughly follows avail-
ability (Fig. 3) , bat predation was unrelated to the
proportion of rodents in the summer diet (r^ =
0.048, N = 8, P = 0.911; Fig. 3). This suggests that
bats are not specifically sought as an alternative
prey. The hypothesis that bats are taken only in
years of marked rodent scarcity also predicts a
clumped occurrence of bats in the diet over the 8

study yr. However, bat occurrence during 31 suc-
cessive seasons did not differ from a random se-
quence (runs test, Zar 1984; Z = 0.726, P = 0.233;
Fig. 3).

Bat remains occurred in 42 pellets (2.1%). In
27% of these, bats were the only prey item, with
2-8 individuals per pellet. In 62% of pellets, bats
occurred together with other prey, but accounted
for ^50% of prey items in each sample. The dis-
tribution of the number of individual bats per pel-
let was aggregated (did not fit a Poisson distribu-
tion with X = 0.055, = 42.62, df = 1, P< 0.001;

only pellets with bats, X = 2.643, = 13.23, df —

3, P = 0.004). These results suggested that bats
were clumped when captured. Pipistrelle bats are

448

Garcia et al.

VoL. 39, No. 4

Figure 1. Localities where Long-eared Owl diet was studied in southern Europe. The broken line separates the
temperate (squares) and the Mediterranean localities (circles) following Emberger et al. (1963). Black circles indicate
sites where bat predation has been recorded. Numbers correspond to study numbers in Table 1.

Table 2. Bat species in the diet of Long-eared Owls in the Mediterranean region of Europe. Seasons when predation
occurred and the range of body mass (g) are also shown. Body masses are from Palomo and Gisbert (2002). Study
number and location are as in Table 1 and Fig. 1.

Species

Body Mass (g)

Season

Source

Study

Greater horseshoe bat

14.6-31.6

Winter

Alivizatos and Goutner 1999

(Rhinolophus ferrumequinum)

All seasons

This study

Greater mouse-eared bat

21.0-35.0

Winter-Spring

Corral et al. 1979

(Myotis myotis)

Fall

Sublimi and Scalera 1991

Lesser mouse-eared bat

18.0-29.5

Spring— Summer

Veiga 1980

{Myotis blythii)

Whiskered bat {Myotis mystacinus)

4.0-8.0

All seasons

Plini 1986

Myotis spp.

Winter

Alivizatos and Goutner 1999

Pipistrellus spp.

3.5-10.0

All seasons

This study

Serotine bat {Eptesicus serotinus)

14.0-33.0

Winter-Spring

Corral et al. 1979

Brown long-eared bat

6.8-12.0

Spring-Fall

Araujo et al. 1974

{Plecotus auritus)

Schreibers’ bat {Miniopterus

10.1-20.8

All seasons

This study

schreibersii)

European free-tailed bat

22.0-54.0

Winter

Alivizatos and Goutner 1999

{Tadarida teniotis)

December 2005

Bat Predation by Long-eared Owls

449

4 -*

Year

I 1 winter i— i spring summer fall

Figure 2 . Temporal variation in the number of individuals taken by Long-eared Owls (bars) and in the percent of
bats in terms of the total number of prey items (line) in Devesa de I’Albufera between 1996 and 2003.

very abundant in the study area and roost in col-
onies, often in buildings. Long-eared Owls could
capture them at emergence as pipistrelle bats leave
the roosts in large groups, but return as single in-

dividuals or in small groups and much more
spaced over time. Although pipistrelle bats do not
gather while foraging over large rice fields, they
can form large aggregations when feeding along

18 n

FWSS FWSS FWSS FWSSFWSS FWSS FWSS FWS
1995 1996 1997 1998 1999 2000 2001 2002 2003

Figure 3. Seasonal variation in the percent (on the total number of prey items) of bats taken by Long-eared Owls in
Devesa de I’Albufera between 1995 and 2003. Below the bars and for each year, shading intensity of cells indicates the
ranked percentage of rodents in the diet, from the highest (dark) to the lowest importance (light) in the seasonal diet.

450

Garcia et al.

VoL. 39, No. 4

drainage channels or near street lamps (Blake et
al. 1994), and the owls could hunt them there as
well. Predation by nocturnal raptors on predictable
accumulations of bats has been previously docu-
mented (Barclay et al. 1982, Fenton et al. 1994,
Hoetker and Gobalet 1999).

The spatial distribution of bat remains during
the owl breeding season was not random. Bat re-
mains appeared in pellets from only five (A^ = 205
prey items) of 16 nests sampled. The mean per-
centage of bats per positive nest sample was 17.6
± 13.0% (SD) of prey items. Only in one owl nest
did bats account for <11% of prey, and the maxi-
mum observed was 37%. These figures make less
plausible the idea of an opportunistic capture of
bats as a result of accidental encounters (Ruprecht
1979) . Our results were consistent with the hypoth-
esis of individual differences in ability to catch bats
or with individual knowledge of the location of pi-
pistrelle colonies, which may be more profitable to
exploit than solitary bat species if the emergence
of large numbers of bats increases hunting success
(Fenton et al. 1994). Even small-sized pipistrelle
bats (body mass = 7.5 g) could be a profitable prey
for Long-eared Owls if available in large quantities.
The biomass of 8 pipistrelle bats (60 g; the maxi-
mum number of bats found per pellet) may satisfy
two thirds of the daily energy needs (93.3 g for a
280 g owl; Wijnandts 1984), perhaps with little en-
ergy expenditure during foraging.

Biogeographic Pattern. We considered 21 diets
for the Mediterranean region (34 410 prey items)
and nine diets in the adjacent temperate region
(22 386 prey items; Fig. 1). In the Mediterranean
region, 38% of diets included bats as prey, whereas
bats did not occur in any diet for the temperate
region (Table 1). These differences in bat occur-
rence were significant (G = 6.885, df — 1, P =
0.009). Even excluding our study in coastal Spain,
where we found an unusually high quantity of bat
remains, the mean proportion of bats in the Med-
iterranean diets was significantly higher than in the
diets of adjacent temperate sites (Mann-Whitney IT-
test, Z = 1.98, P — 0.048). In the Mediterranean
region, the overall importance of bats in the diet
of Long-eared Owls (0.43% of prey-items) was at
least twice as high as in other geographical areas.
But the large number of bats in the diet of owls in
our study area was very influential in this compar-
ison. In fact, omitting our results from eastern
Spain, bats only represent 0.06% of prey items
found in the combined diets from the Mediterra-

nean region, which is similar to figures found else-
where. In the diets from North America (23 888
prey items) and temperate Europe, plus Iraq, re-
viewed by Marti (1976), bats did not occur. In later
reviews, Mikkola (1983) and Speakman (1991)
found that bats accounted for <0.20% of prey
items in Europe (67 805 prey items) and 0.05% in
the British Isles (12 870 prey items).

In the studies we reviewed, bat predation was re-
stricted to latitudes 37— 43°N and altitudes 0—1400
m. Differences between localities in bat occurrence
in the diet could not be attributed to a decline in
bat species richness northwards, as species richness
is almost constant at latitudes 35-50°N in Europe,
which encompass all localities in Figure 1 (Perez-
Barberia 1991, Mitchell-Jones et al. 1999). Howev-
er, bat abundance increases with decreasing lati-
tude and altitude (Perez-Barberia 1991, Kunz and
Fenton 2003). Moreover, following the temporal
pattern of insect availability, bats in Mediterranean
environments show an extended activity season
(Avery 1985, Altringham 1996, Blondel and Aron-
son 1999). Indeed, bat predation occurs in all sea-
sons (Table 2). If an extended period of activity
and a higher abundance were indicators of in-
creased availability of bats for owls, we would ex-
pect increasing bats in the diet with decreasing lat-
itude and altitude. We found no such correlations
(latitude, = —0.05, P= 0.91; altitude, = —0.45,
P = 0.26), but these analyses were based on small
sample sizes {N = 8 diets containing bats) .

Long-eared Owls preyed on nine of 29 bat spe-
cies present in southern Europe (Mitchell-Jones et
al. 1999; Table 2). Speakman (1991) suggests that
large bat species would be more profitable prey
than small ones, and therefore selected by raptors.
However, Long-eared Owls consumed a variety of
bat species, very different in body size, and there
was no bias toward large species (Table 2) . All the
bat species that owls consumed, except Tadarida te-
niotis, forage low in open areas (Altringham 1996),
just as Long-eared Owls do (Mikkola 1983, Tome
2003b) while hunting terrestrial prey on the wing
(Marks et al. 1999). Excluding our results in coastal
Spain, in Mediterranean environments, mean bat
intake per diet, standardized as bats per 1000 prey
items, was 3.4 individuals, suggesting that preda-
tion is in most cases opportunistic (Ruprecht
1979). Comparable results have been obtained for
Barn Owls (Tyto alba; Perez-Barberia 1991), which
are regarded as opportunistic predators of bats.

We conclude that bat aggregations could be a

December 2005

Bat Predation by Long-eared Owls

451

locally important food source for some individual
owls during certain periods, as exemplified by the
population of Devesa de TAlbufera. More gener-
ally, this evidence supports the view that Long-
eared Owls may show substantial trophic plasticity,
in contrast to their widespread recognition as a ro-
dent specialist. In other words, their trophic re-
sponse may be context-dependent rather than im-
posed by morphological or behavioral constraints
that typically affect all populations across the range
of true specialists.

At the geographical scale, bat abundance does
not seem to reflect bat availability for Long-eared
Owls, maybe because hunting strategies for pre-
ferred prey such as rodents are not compatible
with a regular exploitation of flying bats. Accord-
ingly, bats occur in a number of diets across the
Mediterranean region, but their contribution re-
mains largely irrelevant.

Acknowledgments

We thank D. Almenar, M.A. Monsalve, and J. Quetglas
for providing helpful information on bat ecology and R.
Barclay, A, Gastello, D. Tome, and H. Ulmschneider for
valuable comments that improved the manuscript. A.M.
Garcia was supported by a grant from the Conselleria de
Territori i Habitatge, Generalitat Valenciana. A. Rodri-
guez benefited from a research contract by the Conseje-
ria de Educacion, Junta de Andalucia.

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Received 12 August 2004; accepted 3 July 2005
Associate Editor: James R. Belthoff

Short Communications

Differential Effectiveness of Playbacks for Little Owls {Athene noctua)

Surveys Before and After Sunset

Joan Navarro^

Departament de Biologia Animal (Vertebrats) , Facultat de Biologia, Universitat de Barcelona,

Avda, Diagonal 645, 08028 Barcelona, Spain

Eduardo Minguez, David Garcia, Carlos Villacorta, Francisco Botella,
Jose Antonio Sanchez-Zapata, Martina Carrete, and Andres Gimenez
Area de Ecologia, Departamento de Biologia Aplicada, Universidad Miguel Hernandez,
Avda de la Universidad s/n, 03202, Elche, Spain

Key Words: Little Owl, Athene noctua; survey method',

population surveys', playback effectiveness.

Most nocturnal owls respond to broadcast of conspe-
cific recordings, and this technique may be used to study
their behavior (Galeotti and Pavan 1993, Galeotti et al.
1997), to map territories (Finck 1990, Lane et al. 2001),
to identify individuals (Galeotti and Sacchi 2001, Delport
et al. 2002) , or to study population trends (Exo and Hen-
nes 1978, Martinez and Zuberogoitia 2004). Several fac-
tors affecting the effectiveness of playback techniques or
spontaneous vocalizations have been identified, includ-
ing response distance (Proudfoot et al. 2002), season
(Zuberogoitia and Campos 1998), weather (Lengane and
Slater 2002) , gender, and social status (Appleby and Red-
path 1997). However, only a few studies have investigated
systematically how these factors influence playback meth-
odology (McGarigal and Fraser 1985, Redpath 1994, Cen-
tili 2001). When comparing the accuracy of sampling us-
ing spontaneous owl vocalizations or conspecific
playbacks, several authors demonstrated that sampling
error increases when using spontaneous calls (McGarigal
and Fraser 1985, Haug and Didiuk 1993, Redpath 1994).
However, for Eurasian Eagle-Owl {Bubo bubo), passive au-
ditory surveys provide better results than surveys based
on broadcast calls (Penteriani and Pichera 1991, Marti-
nez and Zuberogoitia 2002).

The Little Owl {Athene noctua) is a territorial species
widely distributed in Palearctic regions. This small raptor
inhabits a wide variety of semi-open areas, from steppes
and stony semideserts to farmlands and open woodlands,
and villages and urban areas (Cramp 1985). Little Owls
prey on insects, small mammals, and birds, and hunt
both during diurnal and nocturnal hours (Negro et al.

^ Email address: joannavarro@ub.edu

1990) . Researchers have surveyed Little Owls by listening
to spontaneous vocalizations or by playing typical calls to
provoke the territorial vocalization after sunset (Finck
1990, Exo 1992, Mastrorilli 1997, Zuberogoitia and Cam-
pos 1998, Verwaerde et al. 1999, Pirovano and Galeotti
1999) or before sunset (Martinez and Zuberogoitia
2004) . Territorial defense is performed mostly by males,
which are more vocal than females (Mikkola 1983, Finck
1990, Zuberogoitia and Campos 1998).

Here, we examine the effectiveness of the playback
method to detect Little Owls before or after sunset. Spe-
cifically, we tested whether broadcast before or after sun-
set would elicit the greater response frequency and
whether duration of playback affected the Little Owl re-
sponse rate. We also offer some suggestions to improve
the survey methodology.

Study Area and Methods

We conducted the study in Clot de Galvany Council
Natural Park (southeastern Spain, Province of Alicante).
The study area (ca. 650 ha.) was characterized by a mo-
saic of shrubs, saline grasslands, and mixed forest, inter-
spersed with extensive abandoned arboreal cultures such
as almond and olive trees. The area exhibits a semiarid
Mediterranean climate (Sancho and Lopez 2002).

Between 19 April-17 May 2002 (the courtship and ter-
ritorial defense period; Mikkola 1983, Finck 1990), we
surveyed twice (before and after sunset) for Little Owls
at 14 permanent stations during five sessions (10 d).
Each day, survey stations were sampled with three differ-
ent “survey” experiments, seven before and seven after
sunset. The first survey was made 2 hr before sunset
(1900-2100 H). The second survey was done 2 hr after
sunset (2130-2330 H). These survey experiments were’
(1) Spontaneous Calls: the observer listened for 2 min,
registering the response rate (number of different Little
Owls heard); (2) First Playback: after the spontaneous
calls trial, a territorial intrusion was simulated by broad-
casting territorial calls of Little Owl for 2 min using a

454

December 2005

Short Communications

455

cassette-player. Then, the observer listened for 1 min, re-
cording the response; (3) Second Playback: after the first
playback (1 min later), a new territorial intrusion was
simulated by broadcasting territorial calls for 2 min by
using a cassette-player. The observer listened for 1 min,
recording the total response rate (response rate of first
and second playback) . The sequence of stations surveyed
was reversed every other visit. To reduce the number of
Litde Owls that could be potentially counted twice, the
distances between survey stations were at least 500 m
(Finck 1990, Exo 1992, Centili 2001). To avoid differenc-
es associated with possible bias in sound direction, we
always used the same cassette-player (power: 4 watts, Sony
WN-FX 195, Barcelona, Spain), placed on the ground
with the loudspeakers directed upwards. To minimize the
potential of lower response rates (i.e., owls becoming less
responsive because they habituated to our broadcasts),
we used territorial male calls from five different individ-
ual owls (Roche 1996, SEO 1998, Llimona et al. 2002).
We did not conduct experiments on windy or rainy days.

Because data were not normally distributed, we used
nonparametric tests for statistical analysis (Zar 1996). To
avoid pseudoreplication, we used the mean of response
rate for each survey station. Statistical analyses were car-
ried out using the SPSS statistical package (SPSS for Win-
dows 1999). Two-tailed P-values were used throughout
and statistical significance was set at P < 0.05.

Results

Before sunset, spontaneous Little Owl calls were heard
at only two stations (Table 1). In contrast, Little Owls
were detected after sunset by spontaneous calls at nine
stations (Table 1). As expected, more Little Owls sang
spontaneously after sunset than before (Kruskal-Wallis
test, = 10.39, df = 1, P < 0.001). Numbers of Little
Owls detected by passive auditory surveys were signifi-
cantly lower than those detected by playback surveys,
both before and after sunset (Fig. 1). These differences
were shown in both the comparison with the first play-
back (before sunset: = 22.07, df = 1, P< 0.001; after

sunset: x^ = 19.84, df = 1, P < 0.001), and the second
playback (before sunset: x^ = 28.17, df = 1, P < 0.001;
after sunset: x^ = 25.73, df = 1, P < 0.001). Playback
surveys detected more individuals after sunset than be-
fore (first playback before vs. after sunset: x^ = 6.83, df
= 1, P < 0.001; second playback before vs. after sunset:
X^ = 4.51, df = 1, P = 0.03), but there were no differ-
ences between the two playback experiments within each
period (first playback vs. second playback before sunset:
X^ = 0.55, df = 1, P = 0.46, first playback vs. second
playback after sunset: x^ = 0.03, df = 1, P = 0.87; Fig.
1 ).

Discussion

Our results strongly suggest that nocturnal broadcast
surveys were the most effective method for surveying Lit-
tle Owls, both for detecting presence and counting in-
dividuals or territories (Zuberogoitia and Campos 1998,
Verwaerde et al. 1999, Centili 2001, van Nieuwenhuyse et

2.0 1

Before Sunset After Sunset

Figure 1. Call rates (calling means for Little Owls per
survey station) detected without using playback (sponta-
neous calls) , using first and second playback both before
and after sunset.

al. 2002). These results are in accordance with similar
studies with other owls: Barred Owl {Strix varia; Mc-
Garigal and Fraser 1985), Tawny Owl {Strix aluco; Red-
path 1994), Burrowing Owl {Athene cunicularia; Haug and
Didiuk 1993), Ferruginous Pygmy-Owl {Glauddium brasi-
lianum; Proudfoot and Beasom 1996), and Long-eared
Owl {Asio otus; Martinez et al. 2002).

Interestingly, our study indicated that Little Owls re-
sponded at a similar rate in the first and the second play-
back (before and after sunset). The fact that our first
playback experiment, broadcasting for 2 min, elicited a
similar number of owls as when both playbacks were in-
cluded, suggested that 2 min of continuous playback was
sufficient for detecting Little Owls, which was a shorter
period than that used in other studies of this species (5
min, Zuberogoitia and Campos 1998; 4 min, Verwaerde
et al. 1999; 3 min, Centili 2001).

Detection rate of Little Owls after sunset was less vari-
able and higher than before sunset (Table 1, Fig. 1).
Thus, before sunset, surveys may underestimate the num-
ber of breeding Little Owls in an area. However, the use
of playback before sunset would be useful in finding ter-
ritories and nests because individuals might be observed
when calling at perches (Martinez and Zuherogoitia
2004, pers. obs.).

Estimating the breeding density of owl species is an
important part of population studies, and comparisons
are widely used to assess the abundance of a species
across years and geographical cireas. Biased estimates of
breeding pair density are misleading and prevent com-
parisons between studies. Thus, increased efficiency of
survey methods and knowledge of potential error is nec-
essary. Our results suggest broadcasting 2 min of conspe-

Table 1. Mean call rates (number of different owls calling at each survey station /number of trials ±SD) of Little Owls at Clot de Galvany Park, Alicante Province,
Spain. Data were obtained during five visits/ survey station; protocol included recording spontaneous calls followed by playback of conspecific calls.

456

Short Communications

VoL. 39, No. 4

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cific songs just after sunset elicits vocal responses effec-
tively from resident Little Owls.

Diferente Effectividad del Playback para Censar Mo-
CHUELO EuROPEO {ATHENE NOCTUA ) ANTES Y DESPUES DEL
Anochecer

Resumen. — Los buhos son dificiles de contar pues son
poco conspicuos, tienen habitos nocturnos y duante el
dia permanecen perchados en sitios ocultos. La repro-
duccion de vocalizaciones previamente grabadas ha sido
considerada un modo eficiente para determinar la pre-
sencia de estas sigilosas rapaces. En este estudio exami-
namos la efectividad y precision de la reproduccion de
vocalizaciones para detectar individuos de la especie Athe-
ne noctua. Los censos en los que se reprodujeron llama-
dos espontaneos fueron menos eficientes que aquellos en
los que se reprodujeron vocalizaciones coespecificas pre-
grabadas. La tasa de deteccion luego del atardecer fue
mayor y menos variable que la tasa previa al atardecer.
Esto sugiere que los censos nocturnos con vocalizaciones
podrian ser el metodo mas efectivo para detectar la pre-
sencia de A. noctua y para contar los individuos y terri-
torios de esta especie.

[Traduccion del equipo editorial]

Acknowledgements

We thank Glen Proudfoot, Vicenzo Penteriani, Dries
van Niuwenhuyse, and Dwight Smith for comments on
the previous manuscript. Field work was carried out un-
der permission and with collaboration of the Elche Coun-
cil (Alicante).

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Received 22 November 2004; accepted 31 August 2005

Associate Editor: Cheryl R. Dykstra

458

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VoL. 39, No. 4

King Vultures {Sarcoramphus papa) Forage in Moriche and Cucurit Palm Stands

Marsha A. Schlee^

Museum National d’Histoire Naturelle, Departement Ecologie et Gestion de la Biodiversite, USM 0305, CP 31 Menagerie,

57 rue Cuvier, 75231 Paris cedex 05, France

Key Words: King Vulture, Sarcoramphus papa; Mauritia

flexuosa; Attalea maripa palms, wedge-capped capuchin mon-
keys-, Cebus olivaceus; foraging association.

Feeding on palm fruit, particularly drupes of the Af-
rican oil palm {Elaeis guineensis), has been documented
for several Old World species of birds of prey (Thiollay
1978, Barlow 2004). In the New World, fruits of the im-
ported African oil palm have been consumed by the Tur-
key Vulture {Cathartes aura ruficollis; Pinto 1965), Yellow-
headed Caracara (Milvago chimachima; Haverschmidt
1962), and Black Vulture {Coragyps atratus; Haverschmidt
1947, Pinto 1965, Elias and Valencia 1982). Both vulture
species, as well as the Crested Caracara {Caracara cheri-
way), consume flesh of coconuts {Cocos nucifera; Hav-
erschmidt 1947, Crafts 1968), and fruits of palms {Maur-
itia flexuosa and Desmoncus sp.) have been found in
stomach contents of the Black Caracara {Daptrius ater,
Haverschmidt 1962). American Black Vultures also feed
on sweet potatoes (Mcllhenny 1945) and avocado (Rohl
1949) when carrion is scarce, and Turkey Vultures ingest
leaves, seeds, and bark of cottonwood trees {Populus
spp.), apparently as casting material (Davis 1983). No
published data were found on ingestion of plant matter
by King Vultures {Sarcoramphus papa), but residents at
Hato Las Nieves, Venezuela reported that the species
consumes fruits of the moriche {Mauritia flexuosa) and
cucurit {Attalea maripa) palms when carrion is scarce (Y.
Carbonell and A. Mendoza pers. comm.). The observa-
tions reported in this paper were gathered in an attempt
to verify these claims.

Study Area and Methods

My observations were part of a long-term study (1994-
2000) on the abundance, population structure, move-
ment patterns, and foraging strategies of King Vultures
m the Serranfa de la Cerbatana, Estado Bolivar, Venezue-
la The study was conducted in the southeastern part of
the massif at Hato Las Nieves (Sabana Nueva: 6°34'80"N,
66°12'17'W), a ranch located ca. 125 km south of Caicara
del Orinoco. The valley of Las Nieves, ca. 20 km long
(northwest-southeast) and 9 km wide, is dominated by
lowland shrub savanna, mainly 220-260 m above sea lev-
el. The bordering mountains reach elevations of 1600 m
to the west and 1880 m to the north (Cerro de la Cer-

^ Email address: schlee@mnhn.fr

batana). The moriche palms {Mauritia flexuosa) can be
found scattered in the gallery forests or in stands (mor-
ichales; see Gonzalez Boscan 1987) in the seasonally in-
undated areas of the valley. The moriche fruits, 3-7 cm
long, ovate to globular and having an oily mesocarp
(Borgtoft Pedersen and Balslev 1990), fall to the ground
when almost ripe and accumulate in the water among
fallen fronds and debris. Cucurit palms {Attalea maripa =
Maximiliana regia) occur as stands within the gallery for-
ests on dry terrain. The fruits, ovate, 5-7 cm long, are
also rich in oil (Braun 1997) . The observations reported
here took place during the rainy season, which lasts April
through October or November. The study periods (24
June-24 July 1994, 26 June-14 August 1995, 28 May-14
July 1996, 30 June-18 August 1997) were set up to co-
incide with the fruiting season reported locally for both
palm species. Observations were carried out daily, gen-
erally from 0615-1900 H. The length of each monitoring
period (up to 5 hr) depended on weather, logistics, and
whether or not the King Vultures were present in the
valley. The number of sample days for each study period
varied from 29-50 d, with the afternoon of arrival and
morning of departure being counted if observations were
carried out (Table 1). I used lOX binoculars and ob-
served from outcrops and other high points.

Results

In all four years, moriche and cucurit fruit production
took place earlier than expected and little remained by
mid-July. Both palm species suffered from drought in
1995 and 1996. A mean of 2.1 ± 1.1 (SD) King Vultures
(range = 1-4) foraged in four different morichales {N
= 7 occurrences), and 3.4 ±1.0 (range = 2-4) foraged
{N = 7 occurrences) in two of the cucurit stands, pri-
marily during the 1994 and 1995 field seasons (Table 1).
This activity was most often carried out by two adults to-
gether {N = 5) or three adults and an immature {N =
6), presumed to be the local birds. Eleven of the 14 oc-
currences took place when the vultures had not fed on
livestock carcasses (natural mortality, including jaguar
\Panthera onca] predation) or inedible parts of slaugh-
tered animals for 2—3 wk. Eour bouts in the cucurit stands
(August 1995) followed presumed feeding on the re-
mains of jaguar-killed native wildlife.

On 27 June 1994, at 0947 H, four American Black Vul-
tures flew from the western morichal. As I approached,
I sighted an adult King Vulture perched low at the edge
of the palm stand and another adult on the ground near-

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459

Table 1. Mean number of King Vultures per study period (1994-97) seen foraging in moriche and cucurit palm
stands and number of occurrences at Hato Las Nieves, Venezuela. Number of days the vultures fed on livestock
carcasses and total days of observation are given.

Number of

Study King Vultures

Pebuod X ± SD (range)

Number of Days

Frequency !

Livestock

Moriche Cucurit Carcasses Observation

1994

2.2 ± 1.0 (1-4)

1995

3.3 ± 1.3 (1-4)

1996

3.0 ± 0 (3)

1997

by at the base of the only fruiting moriche in the area.
This bird, with head down, just out of sight, seemed to
be nibbling on something. When both birds flew to near-
by palms, I could see that their crops were extended.
Their flight attracted a Turkey Vulture that walked
around the area but did not feed. At the site, I found
one unripe moriche fruit with half the mesocarp freshly
scraped off longitudinally on one side, the marks clearly
imprinted on the nut, and a large piece of overripe me-
socarp from another fruit. No debris, no carrion, and no
live animals were present. I concluded that the King Vul-
ture had consumed the missing pulp, but this would not
explain crop extension. The next day after the rains
stopped (1620 H), I observed an adult sunning in the
main cucurit stand. As I penetrated into the gallery for-
est, I came across another King Vulture rummaging in
the litter at the base of a cucurit palm. The debris con-
tained no animal matter, only cucurit fruits, whole or rot-
ting or partially eaten, pieces of mesocarp, and clean ker-
nels. Several wedged-capped capuchin monkeys {Cebus
ohvaceus) were in the stand. Two days later (30 June
1994), two adults were observed in a morichal at ca. 1100
H and in a cucurit stand in the afternoon, and the fol-
lowing day three adults and an immature were in the
same cucurit stand at mid-day. Capuchin monkeys were
present both days. The last sighting in 1994 took place
on 7 July, 2 d after the vultures had consumed a dead
horse. At 0737 H an adult was again perched low at the
edge of a morichal. It was raining hard (1000 H) when
1 found the adult foraging under the only fruiting mor-
iche in the area. The bird flushed upon seeing me, but
then returned to the morichal again, weaving in and out
of the vegetation and foraging on the ground as I tracked
it for ca. 90 min. Moriche fruits were present in the areas
where the bird had foraged. I found no carrion or live
animals. The vulture’s crop was extended, indicating it
had ingested food while in the morichal.

On 28 June 1995, at 0722 H, two adult King Vultures
and an American Black Vulture perched at the edge of
a morichal. An hour later another adult King Vulture and
an immature joined them, and one of the first adults flew
to the ground near a palm with fruit. When I investigat-

ed, 1 found several fruits with the mesocarp wholly or
partially scraped off. No carrion was present, but a me-
dium-sized savanna tortoise ( Geochelone carbonaria) was m
the area and could have been feeding on the fruits ear-
lier. Later (1157 H), 1 located the immature bird feeding
at the base of another fruiting moriche. Again, the me-
socarp on several fruits had been freshly scraped off. No
debris or carrion was found, and no live animals were
nearby. 1 concluded that the King Vulture had eaten the
pulp. Two days later, at 0740 H, an adult perched in the
gallery forest north of the central camp, and at 0913 H
I found it foraging on the ground among the few palms
that remained of a remnant morichal. No carrion was
present. On 29 July 1995, 8 d after a carcass had been
consumed, two adults suddenly flew up from one of the
gallery-forest floors (1645 H) in an area that had fruiting
moriche, but 1 was unable to investigate further. Then,
on 5-6 and 9-10 August 1995, three adults and an im-
mature, presumed to be the same birds as above, were
sighted in a cucurit stand. Eight Turkey Vultures were
also present. The King Vultures perched within the up-
per strata of the canopy of the broad-leafed trees, occa-
sionally going to the top of the trees to sun or dry, and
spent the mornings in the stand. A troop of ca. 30 wedge-
capped capuchin monkeys, with many females transport-
ing infants, was foraging there on the first two days. The
area was strewn with large pieces of bark and fallen
branches. On the last 2 d, fewer capuchins were present,
but were seen with a pair of red-howler monkeys {Al-
ouatta seniculus) . 1 found no remains of carrion.

On 8 June 1996 at 0913 H, 4 d after the vultures had
eaten livestock carrion, I came upon two adult King Vul-
tures and an immature resting on a low shrub at the edge
of a morichal and next to a fruiting moriche palm. Three
American Black Vultures were feeding on the ground at
the base of the palm. The crop of one King Vulture was
slightly extended. I found no carrion and no live animals,
only palm fruits lacking part of the mesocarp and show-
ing signs of having been scraped. I concluded that both
vulture species had been feeding on the fruits. This was
the only time the King Vultures were observed to forage
in a morichal in 1996, but very few moriche palms were

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VoL. 39, No. 4

fruiting (<10% in the major stands). No foraging took
place in the cucurit stands, but only two cucurit palms
had fruit, although fermenting drupes were found at the
base of others. Livestock carrion was abundant (Table 1),
and jaguars were in the area.

The King Vultures were not seen foraging in the palm
stands in 1997, even though more moriche and cucurit
were fruiting than in 1996. A small troop of capuchin
monkeys was present twice in the study area, and domes-
tic carrion was not often available (Table 1 ) , as most live-
stock had been removed from the valley. The vultures
picked over the debris at former carcass sites on 1 2 d and
followed a jaguar. This feline was known to have come
through the valley on four occasions, and the King Vul-
tures presumably fed on the remains of kills on native
wildlife at or near Las Nieves on 5 d.

Discussion

My observations support the claims that the King Vul-
tures at Hato Las Nieves eat fruits of the moriche palm,
particularly when carrion is scarce. Eating moriche fruits
may partially compensate the lack of carrion, 100 g of
fresh pulp having 10.5 g of fat and 3.0 g of protein, but
the fruits could have been ingested for their vitamin-min-
eral content (see Gonzalez Boscan 1987, Borgtoft Ped-
ersen and Balslev 1990). From the remains of the fruits
found at the feeding sites, I conclude that the mesocarp
was scraped off longitudinally, but judging from the size
of extended crops of some vultures, some fruits, probably
the smaller ones, may have been swallowed whole. Both
feeding techniques are used by the Palm-nut Vulture ( Gy-
pohierax angolensis) when consuming drupes of the Afri-
can oil and Raphia palms, the ingested kernels being re-
gurgitated later (Thiollay 1978). Only once in my
observations was a potential fallen-fruit consumer pre-
sent — a tortoise. My observations also lend support to
claims that American Black Vultures eat Mauritia fruits
(Y. Carbonell and A. Mendoza pers. comm.). Moriche
fruit-eating appears to be an activity carried out by vul-
tures local to the study area; however, because north-
western Bolivar state is one of the few areas in the Ve-
nezuelan Guayana that has a high concentration of
morichales (see Gonzalez Boscan 1987), moriche fruit-
eating by King Vultures could be more widespread than
at Hato Las Nieves.

On the other hand, I was not able to confirm that King
Vultures eat cucurit fruits, although their consumption is
plausible considering the oil content of the mesocarp
(Braun 1997). Whenever the King Vultures foraged in
the cucurit stands, wedge-capped capuchin monkeys
were also present, which suggests that a foraging associ-
ation may exist between the two species. The monkey
troops were also attended by the Turkey Vultures. Raptor-
monkey associations usually involve opportunistic feeding
on flushed invertebrates, particularly insects (e.g., Fon-
taine 1980), and sometimes on vertebrates displaced by

the movements of monkey troops (e.g., arboreal snakes:
Zhang and Wang 2000) .

How could King Vultures benefit from associating with
Cebus monkeys? Is it only to profit from occasional pri-
mate mortality? Although 55% of the wedge-capped ca-
puchin’s diet consists of plant matter, particularly ripe
fruits, invertebrates are searched out by peeling off loose
bark, digging into rotting material and sifting through
leaf debris on the ground (Robinson 1986). Perhaps the
King Vultures benefit from larvae that are exposed or fall
to the ground while the troop forages; vultures are
known to scoop up maggots from decomposing carcasses
(Houston 1988). Of greater interest is the occasional
predatory behavior of the capuchins on vertebrates. For
example, the viscera of lizards may be eaten but the mus-
cular part left, and the remains of captured frogs dis-
carded (Robinson 1986). In Cebus capucinus, after wres-
tling with an Iguana sp., a monkey managed to break off
30-40 cm of the iguana’s tail, stripped some meat from
it, and dropped the rest (Baldwin and Baldwin 1977) . By
following wedge-capped capuchin monkeys, the vultures
could glean the remains of discarded vertebrate prey.
However, eating moriche fruit or monitoring monkeys
did not seem to be as beneficial as picking over the scat-
tered remains of former carcasses and following jaguars
to consume the remains of kills. These observations il-
lustrate some opportunistic feeding strategies used by
King Vultures.

SaRCORAMPHUS PAPA FORRAJEA EN MORICHALES Y EN GRUPOS
DE Palmas de Cucurto

Resumen. — Este trabajo se realizo durante las epocas llu-
viosas desde finales de junio de 1994 hasta mediados de
agosto de 1997 en la Serrania de la Cerbatana, Hato Las
Nieves, Estado Bolivar, Venezuela. Los datos recolectados
sostienen las afirmaciones del personal del hato de que
Sarcoramphus papas come frutos de la palma moriche
{Mauritia flexuosa), principalmente cuando escasea la ca-
rrona. Una media de 2.1 individuos de S. papa (rango =
1-4) forrajearon en los morichales {N = 7 avistamien-
tos). No pude confirmar las afirmaciones de que S. papa
come tambien frutos de la palma de cucurito {Attalea
maripa). Los frutos de ambas especies de palma contie-
nen aceite. En mis observaciones, una media de 3.4 m-
dividuos (rango = 2-4) se encontraron vigilando tropas
del mono capuchino Cebus olivaceus que habian venido a
forrajear a los rodales de cucuritos. Sugiero que S. papa
podria asociarse con los monos para aprovechar los m-
vertebrados que espantan, como las larvas de insectos,
los restos de vertebrados que capturan y ocasionalmente
los cadaveres de monos.

[Traduccion del autor]

Acknowledgments

I would like to thank my Venezuelan counterparts,
Omar Linares (Universidad Simon Bolivar), the late Jose
Luis Gomez Carredano, and more recently Guilberto

December 2005

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461

Rios (Universidad Nacional Experimental de los Llanos
Occidentales, Ezequiel Zamora) for their advice and sup-
port; Ivan de Angelis and the late Yolanda Carbonell for
allowing this study at Hato Las Nieves; Y. Carbonell and
Alberto Mendoza for their valuable observations;
Susanne Renner (Universitat Ludwig Maximilian, Mu-
nich) for botanical information; and R. Thorstrom, J.
Bednarz, and an anonymous referee for their helpful
comments on the manuscript.

Literature Cited

Baldwin, J.D. and J.L Baldwin. 1977. Observations on
Cebus capucinus in southwestern Panama. Primates 18:
937-941.

Barlow, C.R. 2004. The utilization of oil-palm kernel by
Necrosyrtes monachus in The Gambia. Vulture News 51:
60-62.

Borgtoft Pedersen, H. and H. Balslev. 1990. Ecuado-
rian Palms for Agroforestry. AAU Rep. 23:1-123.
Braun, A. 1997. La Utilidad de las Palmas en Venezuela.

Fundacion Thomas Merle, Carupano, Venezuela.
Crafts, R.C., Jr. 1968. Turkey Vultures found to feed on
coconut. Wibon Bull. 80:327-328.

Davis, D. 1983. Maintenance and social behavior of roost-
ing Turkey Vultures. Pages 322-329 in S.R. Wilbur
and J.A. Jackson [Eds.] , Vulture biology and manage-
ment. University of California Press, Berkeley, CA
U.S.A.

Elias, D.J. and D. Valencia. 1982. Unusual feeding be-
havior by a population of Black Vultures. Wibon Bull.
94:214.

Fontaine, R. 1980. Observations on the foraging associ-
ation of Double-toothed Kites and white-faced capu-
chin monkeys. Auk 97:94-98.

Gonzalez Boscan, V.C. 1987. Los Morichales de los Lla-
nos Orientales. Ediciones Corpoven, Caracas, Vene-
zuela.

Haverschmidt, F. 1947. The Black Vulture and Caracara
as vegetarians. Connor 49:210.

. 1962. Notes on the feeding habits and food of

some hawks in Surinam. Condor 64:154-158.

Houston, D.C. 1988. Competition for food between
Neotropical vultures in forest. Ibis 130:402—417.

McIlhenny, E.A. 1945. An unusual feeding habit of the
Black Vulture. Auk 62:136—137.

Pinto, O. 1965. Dos frutos da palmeira Elaeis guineensts
na dieta de Cathartes aura ruficollis. Hornero 10:276—
277.

Robinson, J.G. 1986. Seasonal variation in use of time
and space by the wedge-capped capuchin monkey, Ce-
bus olivaceus: implications for foraging theory. Smith-
son. Contrib. Zool. 431:1-60.

Rohl, E. 1949. Fauna descriptiva de Venezuela. Bol. Acad
Cienc. Fis. Mat. Nat. 12:1-495.

Thiollay, J.-M. 1978. Les rapaces d’une zone de contact
savane-foret en Cote d’Ivoire: specialisations alimen-
taires. Alauda 46:147-170.

Zhang, S. and L. Wang. 2000. Following of brown ca-
puchin monkeys by White Hawks in French Guiana.
Coredor 102:198-201.

Received 19 July 2004; accepted 18 June 2005

462

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VoL. 39, No. 4

Family Break Up, Departure, and Autumn Migration in Europe of a Family
OF Greater Spotted Eagles {Aquila cij^nga) as Reported by Satellite Telemetry

Bernd-U. Meyburg^

World Working Group on Birds of Prey, Wangenheimstr. 32, D-14193 Berlin, Germany

Christiane Meyburg

World Working Group on Birds of Prey, 31 Avenue du Maine, F-73013 Paris, France

Tadeusz Mizera and Grzegorz Maciorowski
Agricultural University, Zoology Department, Wojska Polskiego 71 C, 60-625 Poznan, Poland

Jan Kowalski

Gugny 2, 19-104 Trzcianne, Poland

Key Words: Greater Spotted Eagle; Aquila clanga; depar-

ture; family break up; migration; satellite telemetry.

The transition of birds of prey to independence is dif-
ficult to study (Brown and Amadon 1968), as both old
and young birds stray ever further from the nest site to-
ward the end of the post-fledging period. We know of no
study concerning a raptor species in which the departure
on migration, the break up of the family, and subsequent
migration have been investigated by satellite tracking.
Here, we report on a case concerning Greater Spotted
Eagles {Aquila clanga) . Available information on this spe-
cies is limited, but Ivanov et al. (1951) and Dementiev
and Gladkov (1951) believed that Greater Spotted Eagle
families departed as a unit on migration.

In the closely related Lesser Spotted Eagle {Aquila po-
marina), both adults migrated separately, as determined
by satellite telemetry (Meyburg et al. 2006). The off-
spring in this species, which were not tracked with satel-
lite telemetry, normally leave before the parent birds.
However, in some cases, the females leave before the
young (Meyburg et al. 2006). Satellite telemetry has so
far been used to track one adult Greater Spotted Eagle
(Meyburg et al. 1995a).

As part of a long-term research program in northeast-
ern Poland (Mizera et al. 2001), we are endeavoring to
raise the level of knowledge, and thereby, the protection
of the Greater Spotted Eagle by making use of the avail-
able technology (i.e., satellite telemetry) to investigate
the species’ migration and wintering habits.

Methods

In 1996, an entire family of Greater Spotted Eagles was
fitted with satellite transmitters (Platform Transmitter

’ Email address: wwgbp@aol.com

Terminals, PTTs) in the Biebrza river valley of northeast-
ern Poland. The eagle nest was located in a National Park
protecting the largest peatlands in Central Europe, in-
cluding 15547 ha of forests, 18182 ha of agricultural
land, and 25 494 ha of wetlands — the Biebrza marshes.
More than 70 natural and semi-natural plant associations
have been documented in the Biebrza valley. The most
dominant forest associations include black alder {Alnus
glutinosa), swampy birch {Betula pubescens) , and peat co-
niferous forests {Salici-Betuletum) . Frequent anthropogen-
ic ecosystems found in the valley are pastures, culdvated
grounds and urbanized areas. One of the greatest threats
to the park is human modified drainage patterns, which
causes the invasion of marshes by shrubs and trees. Active
conservation measures have been applied to stop further
succession and maintain more natural intermediate suc-
cessional stages. A broad public awareness campaign is
in place to encourage the adoption of organic farming,
as 45% of the park is privately owned. The eagle nest was
built in dense humid alder {Alnus glutinosa) and birch
{Betula spp.) forest.

We used the dho gaza method (Hamerstrom 1963,
Clark 1981, Bloom 1987) with a Eurasian Eagle Owl
{Bubo bubo) to trap the adults. By this method, the eagles
“attacked” the live eagle owl, tethered to a perch and
got entangled in the dho gaza net. We used transmitters
supplied by Microwave Telemetry, Inc. (Columbia, MD
U.S.A.) with a mass of 60 g. They were fitted as back-
packs, using Teflon ribbon (Bally Ribbon Mills, Bally, PA
U.S.A.) to attach them to the bird. The young fledgling
eagle was equipped with a battery-powered transmitter
with a mass of 60 g and a temperature sensor. To ensure
as long a life as possible, this radio was programmed to
operate only at intervals of 4 d and then for only 10 hr.
The adult birds were htted with solar-powered PTTs
These were programmed to be in continuous operation,
provided the level of light was sufficient to generate pow-
er for the transmitter.

All location data were analyzed individually and en-
tered into databases. We used the computer program

December 2005

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463

Mapit (Allison 1997) to plot locations, which were pro-
vided by Service Argos, Inc. (Toulouse, France), measure
distances between locations, and trace the migration
routes. This program is an integrated global mapping
and digital display system, which computes the great-cir-
cle distance between one point and another, while dy-
namically displaying both great-circle and constant-com-
pass-bearing (rhumb) lines. Great-circle distances are
physically the shortest distances on a globe.

Results

Three eagles in the family broke up when leaving the
breeding territory. The female was the first to depart (19
September 1996), at least 2 or 3 d before her young. The
male was the last to leave (26 September 1996), 1 wk after
the female. Whereas the adults headed straight for the
Bosphorus (Fig. 1), the 1687 km covered by the young
bird terminated in Albania, where this eagle apparently
perished at the end of October. The young probably left
on 21 or 22 September 1996, and the male was present
on 23 September, but only made minimal migration pro-
gress by midday on 26 September 1996 (Table 1). Due
to the programming of its transmitter (operation of 4 d)
the progress of the young could not be determined as
accurately as that of the two adults. The date of departure
of the young eagle was assessed from the first locations
away from the nest, providing an average estimate of
speed and distance from the breeding territory during
the first stages of its migration (Table 1,2). On average,
this eagle flew only 57 km per day. This young eagle may
have covered the first 257 km up to the first location away
from the nest in more than 4 or 5 d, and thus, have left
the breeding area before 21 or 22 September.

The young bird set off from the breeding territory in
a southwesterly direction (Fig. 1 ) . The eagle remained in
Poland until at least 4 October, while the female and
male were located in the country for the last time on 19
and 26 September, respectively. The female reached the
Bosphorus on 14 October and the male on 22 October.
The young bird apparently met its death in southern Al-
bania, ca. 70 km south of Tirana and 13 km north of
Ballesh. All the data from its transmitter (temperature
and no change of location) after 26 October indicate
mortality. The transmitter was transmitting signals until
13 July 1997. However, it is also possible, but much less
likely, that the eagle lost or removed the transmitter.

Discussion

In birds of prey, the transition to independence is dif-
ficult to study as toward the end of the post-fledging pe-
riod, both old and young birds stray ever further from
the nest site. Direct observation does not account ade-
quately for local movements of raptors as they begin the
departure process. Nevertheless, a number of studies
concerning eagles and other raptors (e.g., Alonso et al.
1987, Morvan and Dobchies 1990, Bahat 1992, Busta-
mante 1995, Real et al. 1998, Rafanomezantsoa 2000)
have been published during recent years.

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464

Short Communications

VoL. 39, No. 4

-52°S

-48°S

-44°S

Figure 1. The autumn migration of the three Greater Spotted Eagles in Europe determined by satellite telemetry
in 1996; dates of arrival at selected points en route are indicated.

December 2005

Short Communications

465

Table 2. The outward migration of the juvenile Greater Spotted Eagle (see Fig. 1) 1996 was determined by satellite
telemetry.

Beginning and
End of
Each Stage"*

Length of the
Different Stages
IN km

Duration
OF Each
Stage (days)

Mean Length
OF Daily Flight
Distances

Countries

Transversed

ca 21/22 Sept
26 Sept: 0044 H

257 km

Poland

26 Sept: 0044 H
30 Sept: 1134 H

Roosting

4.5

—

Poland

30 Sept: 1134 H
4 Oct: 1534 H

242 km

4.5

54 km/day

Poland

4 Oct: 1720 H
9 Oct: 0005 H

76 km

19 km/day

Poland and Slovakia

9 Oct: 0547 H
13 Oct: 0600 H

329 km

82 km/day

Slovakia and Hungary

13 Oct: 0600 H
17 Oct: 1327 H

202 km

4.5

45 km/day

Hungary and Croatia

17 Oct: 1738 H
22 Oct: 0109 H

361 km

90 km/day

Bosnia - Herzegovina

22 Oct: 0109 H
26 Oct: 0619 H

220 km

55 km/day

Montenegro and Albania

Each migration stage was 4 d, based on the duty cycle of the satellite transmitter. Location data provided by Argos Service, Inc
(Toulouse, France).

Dementiev and Gladkov (1951) and Ivanov et al.
(1951) believed that Greater Spotted Eagle families de-
parted together on migration. We know of no study in
the literature on this species, or any other raptor, in
which the dates of departure on migration, the break up
of the family, and their combined or separate migrations
have been investigated by satellite telemetry. The family
of Greater Spotted Eagles studied here clearly broke up
when leaving the breeding territory.

We also have studied a pair of the closely-related Lesser
Spotted Eagle using this method over several years. The
members of this pair migrated separately in 1997—98 and
1998-99 and overwintered ca. 1000 km apart both years
in southern Africa (Meyburg et al. 2006). However, in
this case, the offspring were not tracked.

Registro de la Ruptura Familia, Partida y Migracion
DE Otono de Una Familia de Aquilas Moteadas {Aquila
clanga) en Europa Usando Telemetria Satelital

Resumen. — ^Ambos adultos y el polluelo de una famila de
Aquila clanga fueron estudiados mediante telemetria sa-
tehtal en el noreste de Polonia para determinar la fecha
de inicio de su migracion, la disolucion de la familia y
sus patrones de migracion combinados e independientes.
La familia se disolvio al abandonar el territorio de cria.
La hembra fue la primera en partir, el inmaduro lo hizo
alrededor dos o tres dias mas tarde y el macho partio
una semana despues de la hembra. Los adultos se diri-
gieron directo al Bosforo. El inmaduro recorrio 1687 km

hasta Albania, donde aparentemente murio a fines de
octubre.

[Traduccion del autor]

Acknowledgments

The authors wish to thank the Deutsche Forschungs-
gemeinschaft (DFG) in Bonn, Germany, for its unstinting
financial support of the Satellite Telemetry Greater Spot-
ted Eagle Project, the Polish Environment Ministry in
Warsaw, and the administration of the Biebrza National
Park for kindly allowing us to study and, in particular, to
trap adult birds. We are also grateful to the Poznan Zoo
for providing a live eagle-owl to use as a decoy in trapping
the eagles, to Joachim and Hinrich Matthes, as well as
Mike McGrady, for help in the field, and to Robin Chan-
cellor for linguistic help. Prof. Kai Graszynski kindly
made comments on the first draft of the manuscript, as
well as three anonymous referees.

Literature Cited

Allison, J.B. 1997. Mapit. Version 2.0. Allison Software,
Apollo, PA U.S.A.

Alonso, J.C., L.M. Gonzalez, B. Heredia, andJ.L. Gon-
zalez. 1987. Parental care and the transition to in-
dependence of Spanish Imperial Eagles {Aquila helia-
cd) in Donana National Park, southwest Spain. Ibis
129:212-224.

Bahat, O. 1992. Post-fledging movements of Golden Ea-
gles {Aquila chrysaetos homeyeri) in the Negev Desert,
Israel, as determined by radio-telemetry. Pages 612-

466

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VoL. 39, No. 4

621 in LG. Priede and S.M. Swift [Eds.], Wildlife te-
lemetry: remote monitoring and tracking of animals.
Ellis Horwood Ltd., New York, NYU.S.A.

Bloom, P,H. 1987. Capturing and handling raptors. Pag-
es 99-123 in B.A.G, Pendleton, B.A. Millsap, K.W.
Cline, and D.M. Bird [Eds.], Raptor management
techniques manual. National Wildlife Federation,
Washington, DC U.S.A.

Brown, L. and D. Amadon. 1968. Eagles, hawks and Fal-
cons of the world. Vol. 1. Country Life Books, Felt-
ham, England.

Bustamante, J. 1995. The duration of the post-fledging
dependence period of Ospreys {Pandion haliaetus) at
Loch Garten, Scotland. Bird Study 42:31-36.

Clark, W.S. 1981. A modified dho-gaza trap for use at a
raptor banding station. J. Wildl. Manage. 45:1043-
1044.

Dementiev, G.P. and N.A. Gladkov. 1951. Birds of the
Soviet Union. Moscow, Russia. (In Russian).

Hamerstrom, F. 1963. The use of Great Horned Owls in
catching Marsh Hawks. Proc. Int. Ornithol. Congr. 13:
866-869.

Ivanov, A.I., E.V. Kozlova E.V., L.A. Portenko, and A.Y.
Tugarinov. 1951. Birds of Soviet Union. Vol. 1. Iz-
datelstvo Akademi Nauk SSSR, Moscow, Russia. (In
Russian).

Meyburg, B.-U., X. Eichaker, C. Meyburg, and P. Pai-
LLAT. 1995a. Migrations of an adult Spotted Eagle
tracked by satellite. Brit. Birds 88:357-361.

, C. Meyburg, and J. Matthes. 2006. Annual cycle,

timing and speed of migration of a pair of Lesser
Spotted Eagles {Aquila pomarina) tracked by satellite.
J. Ornithol. In press.

Mizera, T, G. Maciorowski, and B.-U. Meyburg. 2001.
{Aquila clanga (Pallas, 1811) Greater Spotted Eagle]
Pages 145-148 in Z. Glowadnski [Ed.], Polish red
data book on animals. Vertebrates. Panstwowe Wydaw-
nictwo Rolnicze I Lesne, Warszawa, Poland. (In Polish
with English summary).

Morvan, R. and F. Dobchies. 1990. Dependance de jeu-
nes Aigles de Bonelli {Hieraaetus fasciatus) apres I’en-
vol: variations individuelles. Alauda 58:150-162.

Rafanomezantsoa, S.A. 2000. Behavior and range move-
ments during the post-fledging dependence period of
the Madagascar Fish-Eagle {Haliaeetus vociferoides) .
Pages 113-119 inR.D. Chancellor and B.-U. Meyburg
[Eds.], Raptors at risk. Hancock House and WWGBP,
Berlin, Germany.

Real, J., S. Manosa, and J. Godina. 1998. Post-nestling
dependence period in the Bonelli’s Eagle {Hieraaetus
fasciatus). Ornis Fennica 75:129-137.

Received 24 November 2003; accepted 5 September 2005

Seasonal Patterns of Common Buzzard {Buteo buteo) Reiatwe Abundance and Behavior in

PoLLiNO National Park, Italy

Massimo Pandolfi, Alessandro Tanferna, and Giorgia GaibanP
Istituto di Zoologia, Universitd di Urbino, via Oddi 21, 61029 Urbino, Italy

Key Words: Common Buzzard', Buteo buteo; relative abun-

dance] roadside surveys.

Nest-site selection and habitat use have been described
m the Common Buzzard {Buteo buteo) by several authors
(e.g., Penteriani and Faivre 1997, Kruger 2002, Lohmus
2003, Bustamante and Seoane 2004, Sergio et al. 2005),
but few studies have documented annual variations in the
abundance and habitat associations of this species (Meu-
nier et al. 2000).

We conducted monthly roadside surveys of Common
Buzzards in a mountainous area of southern Italy. Al-

^ Present address and corresponding author: Museo di
Storia Naturale, Dipartimento di Biologia Evolutiva e
Funzionale, Universita di Parma, Via Farini 90, 43100
Parma, Italy; e-mail address: gaibani@biol.unipr.it

though roadside surveys have well-known limitations
(e.g., Andersen et al. 1985, Fuller and Mosher 1987, Mill-
sap and LeFranc 1988, Vinuela 1997), they remain a use-
ful technique for monitoring local abundance and distri-
bution of raptors (Fuller and Mosher 1987, Ellis et al.
1990). Because roadside surveys are easy to conduct, they
can be carried out at frequent intervals. Here, we present
results from monthly roadside surveys of Common Buz-
zards. Using these data, we examine habitat associations,
describe seasonal patterns of Common Buzzard behavior
and abundance and, in particular, discuss the effective-
ness of roadside surveys to monitor changes in abun-
dance.

Methods

The Common Buzzard (hereafter buzzard) surveys were
conducted from October 2000-September 2001 in Polhno

December 2005

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467

transects

I — I

Pollino National Park

0,0 4,0 8,0 12,0 16,0 20,0 km

Figure 1. Locations of seven routes (thick dark lines) used for roadside surveys in Pollino National Park, southern
Italy, in 2000-01 (thin lines indicate the boundaries).

National Park (39°58'N, 16°08'E), a 1821 km^ area located
in the southern Italian Apennines (Fig. 1). The elevation
ranges from 170-2266 m. The land uses include farmlands
and oak woods {Quercus ilex, Q. pubescens, Q. cenris) in the
northern section of the park and grassland and beech
woods {Fagus sylvatica) in the southern portion. Over the
study period, the mean monthly temperature was 14.5°C,
with a mean of 28.8°C during July— September and 9.7°C
during October-February. The annual rainfall in the 12
mo of the survey was 841 mm.

We surveyed buzzards along seven paved roads (Fig. 1)
selected randomly with restrictions (Caughley and Sin-
clair 1994). Specifically, we rejected routes adjoining
those roads previously chosen. Each road was surveyed
once each mo, during the third or fourth wk of the mo

and only on calm and clear days. We did not sample on
days with snow, rain, fog, or strong winds. Each month,
the routes were surveyed over 4 d by means of two cars,
each one with a driver and two observers. All surveys
were conducted in the morning (0900-1200 H), typically
the best time to count raptors (Robbins 1981). We drove
at a speed of 40—45 km/hr and stopped the car to con-
firm each sighting. For each buzzard detected, we re-
corded if it was flying or perched and if it was alone or
with other buzzards. Also, we discounted any buzzard that
may have represented a re-sighted bird.

We calculated the relative abundance as the number
of buzzards seen per 100 km sampled. For abundance
computations we excluded the stretches of roads lined by
trees within tunnels, forests, or villages. Therefore, al-

468

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VoL. 39, No. 4

Table 1. Number of Common Buzzards recorded along
seven routes in Pollino National Park (southern Italy,
2000-01). For computation of relative abundance, we
used the survey length obtained discounting the stretch-
es of roads lined by trees or passing through tunnels,
forests, or villages.

Routes

Length
( km) OF

Routes

Survey
Length
( km) OF
Routes

Monthly Mean
±SD OF

Relative Abundance

57.8

40.4

11.2 ± 1.8

18.3

10.2 ± 2.0

44.4

28.9

6.7 ± 2.0

47.3

34.0

12.7 ± 2.7

38.5

38.3

7.7 ± 1.6

43.8

24.2

20.1 ± 5.7

65.1

53.6

9.3 ± 1.2

though the total road length was 315.2 km, we consid-
ered for analysis only 237.6 km (survey km in Table 1).

For the analysis of buzzard habitat associations, we re-
ported the sightings as presence/absence in a 1 X 1 km
UTM grid. We created a 1 km buffer on both sides of
each route and we considered only buzzards observed
inside this buffer. We analyzed the habitat associations
within this buffer using the Corine Land Cover 1:100 000
digital map (Legend level 3, Ministero dell’Ambiente e
del Terri to rio — Ente Parco), identifying 10 land cover
types which we then pooled into four general vegetation
cover types: (1) arable land (cultivated areas regularly
plowed and generally under a rotation system), (2) het-
erogeneous agricultural areas (areas principally occupied
by agriculture, interspersed with natural areas), (3) for-
ests, and (4) shrub or herbaceous vegetation (Table 2).
In each 1X1 km grid cells or portions of a cell included
inside the buffer, we calculated the surface of each cover
type by means of a Geographical Information System
(GIS) analysis (Geomedia Professional 2002). Buzzard
habitat associations were analyzed in four periods: Feb-
ruary-April (courtship), May-July (incubation and nest-
ing), August-September (post-fledging), and October-
January (winter). Although observers recorded the
number of individual buzzards sighted, we only consid-
ered their presence/absence in each grid cell.

We used the Friedman repeated measures analysis of
variance (F,.) to detect any difference in the relative abun-
dance among months and among periods. Using the
same test, we evaluated if the number of flying or
perched buzzards varied among months or periods. We
used the Kruskal-Wallis test to detect any difference in
the relative abundance among routes and the Mann-
Whitney U test to ascertain whether flying buzzards were
observed more frequently than perched buzzards. We
used the arcsin-transformation to convert the proportion
of sightings composed of buzzard groups. The Kolmo-
gorov-Smirnov one-sample test (Z) was used to examine
if the distribution of relative frequencies was uniform.
Finally, we used a stepwise logistic regression to deter-

iso

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Shrub or herbaceous vegetation 0.83 1.14 0.53 1.60 0.20 3.79 0.80 0.84

^ P = statistical significance of the Wald statistic, a chi-square distribution used to ascertain if a variable is a significant predictor of the outcome (presence or absence of buzzards;
Field 2000) .

Exp (B) = indicator of the change in odds (probability of an event occurring divided by the probability of that event not occurring) resulting from a unit change in the predictor
(Field 2000).

December 2005

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469

Figure 2. Monthly mean ±SD of the relative abundance of Common Buzzards recorded along seven routes in
Pollino National Park, southern Italy (2000-01). The dark columns show the relative abundance calculated consid-
ering both grouped and single individuals; the white columns are the relative abundance calculated based on single
individuals only.

mine whether the probability of detecting buzzards var-
ied among the four cover types in each of the periods.
Means are presented ±SD. The nonparametric tests were
from Siegel and Castellan (1988), and the logistic re-
gression analysis followed Field (2000). All of the statis-
tical tests were performed with SPSS 10.0 (SPSS 2000).

Results

During the study period, we recorded 328 buzzard
sightings. The mean relative abundance per roadside sur-
vey was 11.1 ± 4.4 {N = 84) buzzards/ 100 km (Table 1).
Buzzard abundance varied among months {F^ — 23.1; df
= 11; P < 0.05; Fig. 2) and, marginally, among periods
(Fr = 7.6; df = S, P = 0.054). In particular, a post-hoc
multiple comparisons test showed that the abundance
was greater during the courtship period than in the other
three periods and in the incubation-nesting period than
in the winter (P < 0.05 for all comparisons). However,
the relative abundance estimates showed a high variation
for all periods (17.2 ± 11.9 for courtship, 10.2 ± 5.0 for
incubation and nesting, 7.2 ± 4.3 for post-fledging, and
9.0 ± 2.4 for winter).

We found no difference (x^ = 10.3; df = 6; P = 0.11)
in abundance among routes, although the survey routes
crossed different land cover types. We detected more
buzzards flying (87.2%) than perched (12.8%; U = 1.5;
N = 24; P < 0.0001). The number of perched buzzards
did not vary among months (p. = 15.6; df = 11; P >
0.05), whereas the number of flying buzzards did (P^ =
21.0; df = 11; P< 0,05) (Fig. 3), In addition, the number
of flying buzzards varied among periods (p. = 10.8; df =
3; P< 0.05); during courtship, flying buzzards were more
numerous than in all other periods (Multiple Compari-
son test P < 0.05).

Most buzzards detected (67.4%, N = 221) were alone,
while 23.2% {N = 76) were paired and 9.4% {N = 31)
were in larger groups, with a mean group size of 3.9 ±
0.6 individuals. The proportion of sightings composed of
a group of buzzards showed a uniform distribution
throughout the year, ranging from 0.4 in July to 0.0 in
January (Z = 1.5; N= 12; P> 0.05).

No land cover variable entered the stepwise logistic re-
gression discriminating between grid cells with or without
buzzards, in any of the four periods of the year (Table
2 ).

Discussion

The relative abundance of the study population was
relatively stable throughout the year, apart from a peak
during the courtship period (February-April) . A possible
explanation is that during the courtship period, many
young buzzards return to their natal area. A high ten-
dency for philopatric movements among dispersers has
been recorded both in Common Buzzards (Walls and
Kenward 1998) and other raptors (e.g., Ferrer 1993,
Newton et al. 1994, Carter 2001). A second explanation
for the observed increase in relative abundance may be
linked more to buzzard behavior and detectability than
to variations in actual population density. During court-
ship, buzzards participate in more aerial displays than in
other periods, and are thus more detectable. This expla-
nation is supported by the higher proportion of flying
buzzards recorded during the courtship period, particu-
larly in March, when all the detected individuals were
flying (Fig. 3).

The decrease in relative abundance during the incu-
bation and nesting periods is probably related to the fact

470

Short Communications

VoL. 39, No. 4

■o 50

m 40

I 30

o 20

B Flying
□ Perched

IxJ

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Figure 3. Total number of flying and perched Common Buzzards observed per month during vehicle surveys con-
ducted at Pollino National Park, southern Italy in 2000-01.

that half of the breeding population were tending nests
or were close to their nests most of the time. However,
contrary to expectations, during the post-fledging peri-
od, when flying young join the adult population, the rel-
ative abundance was not higher than that estimated dur-
ing the other periods. This could be caused by the
relatively inconspicuous behavior of fledged buzzards
that often are perched in the immediate neighborhood
of the nest for several weeks after fledging (Tubbs 1974,
Tyack et al. 1998). Moreover, because most natal dispers-
al usually occurs in the autumn (Picozzi and Weir 1976,
Walls and Kenward 1998), it is possible that our survey
methods underestimated fledged young during the post-
fledging period.

In our study, buzzards did not show a preference for
any land cover type during any periods of the year. This
is supported by lack of variation among the seven road-
side surveys, although these routes crossed different hab-
itats. This lack of association with cover type may be due
to the buzzard’s high plasticity and varied diet (Cramp
and Simmons 1979, Sergio et al. 2002). However, San-
chez-Zapata and Calvo (1999), Kruger (2002), and Sergio
et al. (2005) found that buzzard breeding sites were
linked to some landscape characteristics, particularly for-
est cover. There are three possible explanations for this
discrepancy in results. First, the previous studies exam-
ined the relationship between habitat characteristics and
nesting sites, while we examined the association of indi-
vidual locations with land cover type. Second, we record-
ed buzzards when in flight or perched, whether they were
hunting or involved in other activities. Finally, the dis-

agreement could be related to the coarse scale of our
landscape analysis. However, Sanchez-Zapata and Calvo
(1999) found a linkage between buzzard nest sites and
some landscape characteristics using a coarse-scale (1.
200 000) land use map.

In summary, our results showed that the relative abun-
dance of a raptor population recorded by road counts
may be sensitive to temporal behavioral changes, which
ultimately affect detectability, thus biasing a potential as-
.sessment of seasonal variations in numbers. For this rea-
son, roadside surveys would be a coarse method to mon-
itor intra-annual population changes, or to compare the
relative abundance recorded in different years, unless the
data are collected in the same time period or season. On
the other hand, we suggest further investigation into
whether roadside surveys can be a useful tool for long-
term monitoring of a population when comparing the
same months in different years.

Patrones Estacionaits en ia Abundancia Relativa y el

COMPARTAMIENTO DE BUIEO BUTEO EN EL PARQUE NACION-
AL POLl.INO, ItAUA

Resumen. — Se estudio la abundancia relativa de una po-
blacion de Buteo buteo a lo largo de 12 meses en el Parque
Nacional Pollino (sur de Italia) para comparar datos en-
tre meses y para determinar las asociaciones de habitat
Realizamos censos mensuales en carreteras a lo largo de
siete rutas (total = 315 km). La media anual de aves
detectadas fue de 11.1 ± 4.4 individuos/100 km, aunque
este valor vario significativamente entre meses. Esta varia-

December 2005

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471

cion probablemente reflejo la actividad de vuelo de B.
buteo y no las fluctuaciones en el niimero de individuos
durante el ano, ya que la mayoria de los registros tuvie-
ron lugar durante el periodo de cortejo. Con base en
nuestros resultados, sugerimos que los censos realizados
para esta especie a lo largo de carreteras son mas efec-
tivos durante el periodo reproductivo que en otras epo-
cas, cuando los individuos realizan vuelos elevados con
menor frecuencia. Finalmente, la presencia y la distri-
bucion de B. buteo dentro del parque no se asociaron con
el tipo de cobertura del suelo.

[Traduccion del equipo editorial]

Acknowledgments

We are indebted to Pollino National Park, which pro-
vided support for this project. We are grateful to P. Perna
for GIS analysis and to A. Aradis, B. Carelli, E. Giardi-
nazzo, N. Pantone, L. Paternostro, R. Rotondaro, P. Sto-
rino, and S. Urso for their help in the field data record-
ing. We thank N.E. Seavy, F. Sergio, and G. Boano for
their comments on an early draft of the paper.

Literature Cited

Andersen, D.E., O.J. Rongstad, and W.R. Mitton. 1985.
Line transect analysis of raptor abundance along
roads. Wildl. Soc. Bull. 13:533-539.

Bustamante, J. and J. Seoane. 2004. Predicting the dis-
tribution of four species of raptors (Aves: Acdpitridae)
in southern Spain: statistical models work better than
existing maps./. Biogeogr. 31:295-306.

Carter, I. 2001. The Red Kite. Arlequin Press, Chelms-
ford, Essex, England.

Caughley, G. and A.R.E. Sinclair. 1994. Wildlife ecology
and management. Blackwell Science, Cambridge,
England.

Cramp, S. and K.E.L. Simmons [Eds.]. 1980. Handbook
of the birds of Europe, the Middle East, and North
Africa. The birds of the western palearctic. Vol. II.
Hawks to Bustards. Oxford University Press, Oxford,
England.

Ellis, D.H., R.L. Glinski, and D.G. Smith. 1990. Raptor
road survey in South America. J. Raptor Res. 24:98-
106.

Ferrer, M. 1993. Juvenile dispersal behavior and natal
philopatry of a long lived raptor, the Spanish Imperial
Eagle. Ibis 134:128-133.

Field, A. 2000. Discovering statistics using SPSS for Win-
dows. SAGE Publications, London, England.

Fuller, M.R. and J.A. Mosher. 1987. Raptor survey tech-
niques. Pages 37—65 in B.A. Pendleton, B.A. Millsap,
K.W. Cline and D.M. Bird [Eds.], Raptor manage-
ment techniques manual. Nat. Wildl. Fed., Washing-
ton, DC U.S.A.

Geomedia Professional. 2002. Geomedia Professional
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Kruger, O. 2002. Analysis of nest occupancy and nest
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Lohmus, a. 2003. Are certain habitats better every year?
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Meunier, F.D., C. Vereyden, and P. Jouventin. 2000. Use
of roadside by diurnal raptors in agricultural land-
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Millsap, B.A. and M.N. LeFranc, Jr. 1988. Road transect
counts for raptors: how reliable are they? /. Raptor Res.
22:8-16.

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Penteriani, V. and B. Fatvre. 1997. Breeding density and
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SAnchez-Zapata, J.A. and J.F. Calvo. 1999. Raptor distri-
bution in relation to landscape composition in semi-
arid Mediterranean habitats. / Appl. Ecol. 36:254—262

Sergio, R, A. Boto, C. Scandolara, and G. Bogliani.
2002. Density, nest-sites, diet, and productivity of
Common Buzzards {Buteo buteo) in the Italian pre-
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Penteriani. 2005. Effect of agro-forestry and land-
scape changes on Common Buzzards {Buteo buteo) m
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Siegel, S. and N J. Castellan, Jr. 1988. Nonparametric
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Received 7 October 2004; accepted 5 September 2005

Associate Editor: Fabrizio Sergio

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VoL. 39, No. 4

New Nesting Record and Observations of Breeding Peregrine Falcons

IN Baja California Sur, Mexico

Aradit Castellanos, 1 Cerafina Arguelles, Federico Salinas-Zavala, and Alfredo Ortega-Rubio
Centro de Investigaciones Biologicas del Noroeste, S.C. Apdo. Postal No. 128 CP 23000,

La Paz, Baja California Sur, Mexico

Keywords: Peregrine Falcon-, Falco peregrinus; nesting re-

cord-, Baja California-, Mexico.

The B^a California peninsula has been an area where
resident Peregrine Falcons {Falco peregrinus) were com-
mon in the past (Bancroft 1927, Banks 1969). Historical
records of their presence in the region were published
by Bryant in 1889 (see Grinnell 1928). Detailed accounts
of nesting territories for the peninsula and Gulf of Cali-
fornia islands were made by Banks (1969), Anderson
(1976), and Porter et al. (1988). According to Banks
(1969), prior to 1967, 54 known peregrine locations ac-
counted for approximately 66 nest sites in this region.
Porter et al. (1988) identified 67 eyries in this area in
1976-84. As in other parts of the world from the late
1960s to the early 1980s, the peninsular Peregrine Falcon
population declined, likely due to the impact of organ-
ochlorine pesticides (Kiff 1988). However, published data
show that recovery began by the late 1980s (Porter et al.
1988, Castellanos et al. 1997).

Historical nesting territories were mainly located on
sea cliffs of the western side of the state of Baja Califor-
nia, from Tijuana to Santa Catarina, and on islands along
both coasts of the peninsula (Banks 1969, Porter et al.
1988, Castellanos et al. 1997, Ruiz-Campos and Contrer-
as-Balderas 2000). A small number of inland territories
were also known (Banks 1969, Castellanos et al. 1997).
However, no nesting pair has ever been reported on Ba-
hia Magdalena region, which is located on the west coast
of the peninsula (Fig. 1). Here, we provide the first re-
port of Peregrine Falcons nesting in this area. Our find-
ing extends the breeding range of this species to an area
of the Baja California peninsula lacking suitable natural
nesting sites. We also report on the reproductive output
of this pair.

Methods

We observed the nest from vantage points 100-200 m
from the metal tower, where the peregrine nest was lo-
cated. We monitored activities around the nesting area,
and with the help of binoculars and a spotting scope,
recorded the behavior and attendance of adults at the
nest. During each observation period, we registered the

^ Email address; arcas04@cibnor.mx

contents in the nest, the birds’ activities, time, the num-
ber of interactions between birds, and disturbance events
that occurred.

Results and Discussion

On 25 January 2004, we found a pair of Peregrine Fal-
cons at 25°05'2T'N and 112°04'41"W in Santa Elenita, a
remote, abandoned industrial port 7 km north of Adolfo
Lopez Mateos in Bahia Magdalena, Baja California Sur,
Mexico. Both birds displayed activities (mutual roosting,
cooperative hunting excursions, courtship flights) sug-
gesting they were a territorial pair. The same day we
sighted another single adult Peregrine Falcon 7.5 km
south of Santa Elenita. After our finding, we visited Santa
Elenita between February to mid-October to monitor the
pair’s reproductive status (20 hr 25 min of observation
in 9 d between 1000-1600 H). The port is a concrete
platform about 30 m wide by 120 m long located in a
mangrove estuary. Above this platform there are four
metal towers and a central crane 40 m tall. The crane
has a metal horizontal arm about 30 m long oriented
northeast to southwest (Fig. 2). The peregrine pair nest-
ed on an old Osprey {Pandion haliaetus) nest at the ex-
treme southwestern end of the arm (Fig. 2). On the op-
posite side was another Osprey nest. A small fishing camp
near the platform was operating daily during the study.

On 28 February, we saw another single bird (male Per-
egrine Falcon, by relative size) approaching the nest.
Both males “fought,” and after the interaction and the
intruder left, the nesting male copulated with the female.
On 18 March, we found the female incubating eggs.
From 8-28 May, three nestlings were observed in the
nest, and they began to fly in late June. On 22 July, we
observed the parents and one of the fledglings. The
adults were still on the territory on 1-4 and 11-15 Oc-
tober.

The tower was shared with an Osprey pair during the
entire study period. However, both pairs showed toler-
ance despite their proximity. Daily and incidental human
disturbance at the hase of the towers was relatively in-
tense (22 events or 1.08 events/hr, including small boats,
people, cars, and motocross traffic); however, the pere-
grine nest was not deserted and breeding was successful.
Peregrine response to disturbance occurred more fre-
quently when other birds approached to within about 20

December 2005

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473

Figure 1. Current and historical distribution of nesting territories of Peregrine Falcon in Baja California Sur, Mexico

474

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VoL. 39, No. 4

Figure 2. View of Santa Elenita mangrove estuary in Bahia Magdalena, B. C. S., Mexico, and Peregrine Falcon (a)
and Osprey (b) nesting sites.

m of the nest. We observed 16 interactions (0.79 events/
hr), including eight with Magnificent Frigatebirds {Fre-
gata magnificens ) , four with Ospreys, three with Common
Ravens {Corvus corax), and one with a gull {Larus sp.).
Peregrines made territorial attacks or cacking-calls in all
interactions.

Breeding dates and the number of nestlings and fledg-
lings reared by this p£iir were similar to those reported
for other areas on the western coast of the peninsula
(Porter et al. 1988, Castellanos et al. 1997). Previous re-
ports (Castellanos et al. 1997) also show the number of
nestlings and fledglings produced by pairs on the western
side of the peninsula are greater than those along the
Gulf of California. Reasons for this higher productivity
are unknown. However, it may be an indication of a
healthier environment; the west coast of the peninsula is
a relatively low organochlorine pesticide-polluted area in
North America (total DDT concentration levels on Os-
prey eggs between 5-311 ppm lipid basis; Spitzer et al.
1977).

The southwest coastline of the peninsula is quite dif-
ferent from the northwestern coast. The terrain is rela-
tively flat and covered by sparse desert shrubs. The lack
of suitable natural nesting sites such as sea cliffs, ledges
on vegetated slopes, and high trees precludes establish-

ment of breeding pairs in spite of a variety and abun-
dance of shore birds and waterfowl. The Santa Elenita
towers provided an opportunity for this nest-site-limited
species to breed.

Future conservation of Peregrine Falcon south of the
U.S.A. should be focused on protection of the natural
landscape (Temple 1988). This strategy is on course in
Mexico. In 1972, the islands in the Gulf of California
were protected as wildlife refuges. In 1988, the entire
central west coast, including the small islands and Lagun-
as Ojo de Liebre and San Ignacio, was declared a bio-
sphere reserve. These refuges preserve prime Peregrine
Falcon breeding range with low human impact.

Nuevo Registro de Anidacion y Observaciones de Hal-
coNES Peregrines Reproductores en Baja Caufornia
S uR, Mexico

Resumen. — Encontramos una pareja reproductiva y dos
adultos no reproductivos de Falco peregrinus en Bahia
Magdalena, en la costa suroeste de Baja California Sur,
Mexico. El nido estaba localizado en una torre metalica
en un puerto abandonado. La anidacion fue exitosa y
tres volantones abandonaron el nido. Nuestro hallazgo
amplia el rango de anidacion conocido en la peninsula.

[Traduccion de los autores]

December 2005

Short Communk:ations

475

Acknowledgments

We thank A. Cozar, A. Ortiz, E. Rivera, and P. Tamez
for field assistance. Financial support was provided by
Centro de Investigaciones Biologicas del Noroeste, S. C.
and Secretaria del Medio Ambientes y de los Recursos
Naturales-Consejo Nacional de Ciencia y Tecnologia proj-
ect 2002-GO 1-0844. We are grateful to Jim Watson, Tom
Cade, and one anonymous reviewer for their comments
on an earlier draft of this paper. Thanks to Dr. E. Glazier
for editing the English-language text.

Literature Cited

Anderson, D.W. 1976. The Gulf of California, Mexico.
Pages 270-271 in R.W. Fyfe, S.A. Temple, and T.J.
Cade [Eds.], The 1975 North American Peregrine
Falcon survey. Can. Field-Nat. 99:228-273.

Bancroft, G. 1927. Notes on the breeding coastal and
insular birds of central Lower California. Condor 29:
228-273.

Banks, R.C. 1969. The Peregrine Falcon in B^ya Califor-
nia and the Gulf of California. Pages 81—91 in JJ-
Hickey [Ed.], Peregrine Falcon Populations. Univer-
sity Wisconsin Press, Madison, W1 U.S.A.
Castellanos, A., F. Jaramillo, F. Salinas, A. Ortega-Ru-
BIO, AND C. Arguelles. 1997. Peregrine Falcon recov-
ery along the west central coast of the Baja California
peninsula, Mexico./, Raptor Res. 31:1-6.

Grinnell, J. 1928. A distributional summation of the or-
nithology of Lower California. Univ. Calif. Publ. Zool.
32:1-300.

Kief, L.F. 1988. Changes in the status of the peregrine in
North America: an overview. Pages 123-139 in T
Cade, J. Fnderson, C. Thelander and C. White [Eds.],
Peregrine Falcon populations: their management and
recovery. The Peregrine Fund, Inc., Boise, ID U.S.A.

Porter, R.D., M. A. Jenkins, M.N. Kirven, D.W. Anderson
AND J.O. Keith. 1988. Status and reproductive perfor-
mance of marine peregrines in Baja California and
the Gulf of California, Mexico. Pages 105-114 in T.
Cade, J. Fnderson, C. Thelander and C. White [Eds.],
Peregrine Falcon populations: their management and
recovery. The Peregrine Fund, Inc., Boise, ID U.S.A.

Ruiz-Campos, G. AND AJ. Contreras-Balderas. 2000.
New northern nesting record of the Peregrine Falcon
in Baja California, Mexico./. Raptor Res. 34:151.

Spitzer, P.R., R.W. Risebrough, J.W. Grier, and C.R. Sin-
DElAR, Jr. 1977. Eggshell thickness-pollutant relation-
ships among North American Ospreys. Pages 13—19
mJ.C. Ogden [Ed.], Trans. North American Osprey
research conference. U.S. Nat. Park Serv. Proc. Ser. 2,
Washington, DC U.S.A.

Temple, S.A. 1988. Future goals and needs for the man-
agement and conservation of the Peregrine Falcon.
Pages 843-848 in T. Cade, J. Fnderson, C. Thelander
and C. White [Eds.], Peregrine Falcon populations:
their management and recovery. The Peregrine Fund,
Inc., Boise, ID U.S.A.

Received 7 December 2004; accepted 5 September 2005

Associate Editor: James W. Watson

Letters

A Previously Undescribed Vocalization of the Northern Pygmy-Owl

Vocalizations of the Northern Pygmy-Owl {Glaucidium gnoma) were summarized by Holt and Peterson (2000, The
Birds of North America, No. 494, Philadelphia, PA U.S.A.). The known repertoire of adult vocalizations consists of:
the “toot song,” which functions as the primary song for both sexes; the “trill call,” which often accompanies the
“toot song” and for which a function is not yet known; and the “chitter call,” which accompanies prey deliveries
and certain interactions between breeding adults. Also, a “chatter call” used during copulation was described by
Righter (1995, Colo. Field Ornithol. J. 29:21—23). Here, I describe a previously undocumented vocalization of the
Northern Pygmy-Owl.

As part of an ongoing study of Northern Pygmy-Owls in northern Montana, I have radio-tracked 11 (between one
and five annually) owls since 2001. Owls were tracked before, during, and after the nesting season. Periods of
behavioral observation were intermittently conducted in durations ranging from ca. 15 min to 4 hr. On three occa-
sions, I observed a “weet” vocalization, which somewhat resembled a single note of the “toot song,” but was slightly
prolonged with a “screeching” quality and a slight upward bend in pitch. In abruptness and duration, this call
superficially resembled the sudden, high-pitched alarm calls of some Spermophilus ground squirrels, but was deeper
in pitch and slightly more hollow sounding. The most similar avian call that I am familiar with is the ksew call of the
Northern Saw-whet Owl {Aegolius acadicus; Cannings 1993, The Birds of North America, No. 42, Washington DC,
U.S.A.). However, that call is lower in pitch, descending, and usually repeated in a brief series, while the weet call I
describe here was a single ascending note. Proudfoot and Johnson (2000:7, The Birds of North America, No. 498,
Philadelphia, PA U.S.A.) describe an alarm call of the congeneric Ferruginous Pygmy-Owl {Glaucidium brasilianum)
as “short and sharp with upward inflection, pee weet, repeated at irregular intervals.” Although I am unfamiliar with
the Ferruginous Pygmy-Owl alarm call, this describes accurately the Northern Pygmy-Owl vocalization I observed,
except that the former consists of two syllables and the latter only one.

On 21 July 2003, while observing a Northern Pygmy-Owl family group, I first observed an adult male give the
''iveet" call. A few seconds later an adult Northern Goshawk {Accipiter gentilis) flew within 50 m of the family group
and disappeared. On 1 July 2004 at 0936 H, while observing a family group with recently fledged young, I observed
both the adult male and adult female give the weet call. A Northern Goshawk appeared and perched briefly in the
same stand as the family group a few seconds after the calls. In that instance, the male gave the call first and was
followed by the female. The female then repeated the call one more time just before the goshawk entered the stand
The female’s call was slightly higher pitched to a degree approximately equivalent to the difference in pitch of the
“toot song” between the .sexes (Holt and Peterson 2000, pers. obs.). At 1003 H, during the same observation period
on 1 July 2004, a Northern Goshawk flew through an opening adjacent to the stand in which the family group (same
stand and same family group as the previous observation) was located. Both adults gave weet calls, and both repeated
the calls after 5—10 sec. In that instance, several of the seven fledglings had been calling actively before the adults
gave the weet calls. The fledglings’ calls immediately ceased after the weet calls were given, but resumed less than 30
sec later, at which time the goshawk was no longer visible to me. 1 am not certain whether any of the Northern
Goshawks in these instances were aware of the owls. Twice the goshawks simply flew past, and the one time a goshawk
perched nearby, it quickly left the perch when it apparently became aware of my presence. The contexts of these
observations suggest that the function of the weet call is an alarm call. During a Northern Pygmy-Owl study in
Washington, A. Giese (unpubl. data) observed what was likely the call described here, and likewise suspected its
function as an alarm call. The call was given several times during a 1.5 hr period by an adult female in the presence
of fledged young. The young generally ceased vocalizing after the call was given. Unlike the calls I observed, however,
that female vocalized in bouts of 3-4 calls at a time.

Interestingly, I have observed instances in which Northern Pygmy-Owls might have been expected to give alarm
calls, but did not give the weet call. I observed a domestic dog in close proximity (<5 m) to a group of fledgling and
adult owls perched low on branches on two occasions in 2004 and heard no calls. When banding young owls or
climbing nest trees to check nests, I have observed adults give short versions of the toot song, trill calls, and display
agitated behavior (e.g., rapid tail twitching, perching close to and staring at the human intruder). However, I have
not heard the weet call I describe here in those situations. On 7 May 2001, I observed a Northern Goshawk pass

476

December 2005

Letters

477

within 5 m of a solitary nonbreeding Northern Pygmy-Owl perched with prey. The owl watched the goshawk intently,
but gave no call.

If the weet call was indeed an alarm call, these observations suggested that it may be associated specifically with
avian predators, as the mammalian (dog and human) observations I described did not elicit the call. Additionally,
the observation of the solitary owl failing to give a weet call suggests that it may be used only when fledglings or
mated owls are present. Alarm calls are well documented for many strigids (e.g.. Ferruginous Pygmy-Owl, Proudfoot
and Johnson 2000; Great Gray Owl, Strix nebulosa, Bull and Duncan 1993, The Birds of North America, No. 41,
Philadelphia, PA U.S.A.; Long-eared Owl Asio otus, Marks et al. 1994, The Birds of North America, No. 133, Phila-
delphia, PA U.S.A.) and are often given in response to threats to nests and fledged young. However, further study is
needed to better understand the causes and contexts of this and other Northern Pygmy-Owl vocalizations.

I am grateful to the many individuals who have volunteered their time to conduct fieldwork during this study.
Private contributions have helped make this ongoing study possible. The Conservation Research Foundation, Mar-
mot’s Edge Conservation, the Owl Research Institute, and the Rocky Mountain Ranger District of the Lewis and
Clark National Forest have generously provided assistance with various parts of this project as well. A. Giese and G
Proudfoot provided criticism and field observations that improved the manuscript. — Graham G. Frye (e-mail address:
ggfrye@rmf-inh,org) Rocky Mountain Front Institute of Natural History, P.O. Box 186, Ghoteau, MT 59422 U.SA.

Received 12 August 2004; accepted 18 June 2005
Associate Editor: Ian G. Warkentin

BOOK REVIEW

Hawks and Owls of Eastern North America. By

Donald S. Heintzelman. 2004. Rutgers University
Press, Piscataway, NJ U.S.A. viii + 203 pp., 5 color
plates, numerous black and white photos. ISBN
0-8135-3350-3. Cloth, $29.95.— Donald Heintzel-
man ’s original purpose with this volume was to pre-
pare a second edition of his earlier work, Hawks
and Owls of North America (1979, Universe Books,
New York, NYU.S.A.). However, this book restricts
coverage to the raptors of eastern North America,
which is loosely defined as birds east of the Missis-
sippi River, except for parts of Minnesota and On-
tario. The volume begins with six chapters dealing
with general topics: Introduction to Raptor Ecolo-
gy, Hawk Migrations, Owl Migrations and Inva-
sions, Raptor Conservation, Citizen Scientists, and
Recreational Raptor Watching; and follows with
eight chapters of raptor species accounts mostly in
taxonomic order, beginning with Ospreys {Pandion
halieatus) and ending with Northern Saw-whet Owls
{Aegolius acadicus). For the most part, the book is
nicely illustrated with a selection of outstanding
black and white photos.

I found the introductory chapter, “An Introduc-
tion to Raptor Ecology,” to be well out of date. In
the preface, Heintzelman acknowledges that this
chapter includes substantial portions of the text
from his 1979 contribution. Upon reading this
chapter, it is clear that many of the ideas expressed
reflect antiquated ecological opinions and specu-
lations of the 1960s and early 1970s. Statements
such as. Northern Goshawks {Accipiter gentilis) are
beneficial to Ruffed Grouse (Bonasa umbellus) pop-
ulations, that raptors control numbers of prolific
rodents, and raptors maintain a delicate and effec-
tive ecological balance between predator and prey,
without presentation of supporting data or sources
are made freely throughout this short chapter.

The subsequent introductory chapters, although
brief, provided easier reading and were based on
more-current information. The chapter on Raptor
Conservation reported a series of interesting and
relatively-recent anecdotes. However, when discuss-

ing habitat degradation and loss, Heintzelman em-
phasizes the “ambitious, long-term restoration” ef-
fort of the Lehigh Gap Restoration Project, which
has a goal of restoring 750 acres of woodland on
the Kittatinny Ridge in Pennsylvania. From a rap-
tor perspective, restoring ca. 3 km^ of deciduous
woodland habitat is extremely trivial and will likely
have little impact on the population of any raptor.
I am familiar with several other governmental and
private (e.g., the Nature Conservancy) land acqui-
sition/habitat restoration programs that involve
many thousands of hectares that are much more
likely to have substantial population impacts on
several species of raptors. I would have liked to
have seen Heintzelman discuss some of these ma-
jor habitat restoration efforts, perhaps in addition
to smaller isolated projects that he has personally
spear-headed.

Some minor distractions for me were the provi-
sion of selective contact information. Although
most major raptor conservation organizations were
mentioned in the volume, contact information was
only provided for a select few. Perhaps, in this day
and age in which an interested person can quickly
obtain contact information by googling the name
of an organization, this is not necessary. But, why
provide detailed contact information (postal ad-
dress, e-mail address, phone numbers) for a few
selected organizations, and no information for oth-
ers?

Probably more bothersome for a professional or-
nithologist using this volume is the style of not cit-
ing references in the text. Although most chapters
are reasonably-well researched and supported with
references, albeit selectively, all references are in-
cluded in the back of the volume listed alphabeti-
cally by chapter. Thus, when you encounter a state-
ment in a given chapter, identifying the
responsible source is exceedingly difficult. Also,
the supporting sources represent a very mixed bag
in which some very current and important studies
are mentioned and cited, while most of the refer-
ences are from state journals and generally repre-
sent novel anecdotes.

Although I found most of the material presented
in the species accounts to be accurate, I ran across
several reported “facts” that in my opinion.

478

December 2005

Book Review

479

amounted to unsubstantiated and rather far-reach-
ing speculations. Some examples include a state-
ment that evidence supports that mated pairs of
Rough-legged Hawks {Buteo lagopus) perch togeth-
er on their wintering grounds; statements or im-
plications that several species of raptors covered in
the volume relatively commonly exhibit coopera-
tive hunting; that Gyrfalcons {Falco rusticolus) are
faster than Peregrine Falcons {F. peregrinus); and
that the food habits of several small raptors include
large birds and mammals, such as waterfowl (An-
atidae), grouse (Tetraoninae) , raccoons {Procyon lo-
tor), woodchucks (Marntota monax), and hares (Le-
pus spp.). The latter is true, although most of these
relatively large preys are taken rarely and most like-
ly involve very-young animals or carrion. This clar-
ification is generally not included and the way ac-
counts are worded, the text implies that such large
prey are just as commonly taken as small rodents.
The layout of the book, with citations lumped by
chapter, makes tracking down the specific sources
for these far-reaching speculations and implica-
tions nearly impossible. As a scientist, I found this
aggravating.

Besides my mild complaints indicated above, the
species accounts were concise and informative.
Within each account, the known longevity record
for each species is reported, which I found to rep-
resent an interesting anecdote. Each account is il-
lustrated with one or more high-quality black and
white photos of the featured species. For the most
part, the volume is well-edited and I found only a
few typographical errors scattered about the text.

Generally, I feel this volume would make an ex-
cellent primer for an amateur or beginning stu-
dent interested in North American birds of prey.
The presentation of the basic natural history and
promotion of recreational hawk watching to the
beginning student of birds is clearly the intended
target of this publication. I would recommend tbis
volume to a high school or underclass university
student that expresses an interest in raptors. Also,
this book would make an excellent resource for
local public libraries throughout eastern North
America. — James C. Bednarz, Department of Bio-
logical Sciences, Arkansas State University, P.O.
Box 599, Jonesboro, AR 72467 U.S.A.

Journal of Raptor Research

INFORMATION FOR CONTRIBUTORS

The Journal of Raptor Research (JRR) publishes
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482

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[photographs] . CONSULT THE EDITOR IN AD-
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More information:

Telephone: (513) 779-1744

E-mail: journalofraptorresearch@juno.com

Index to Volume 39

Prepared By Autumn A. Farless

The index includes references to general topics, common names, keywords, and authors. Reference is also made
to book reviews and letters. Taxa other than raptors are included where referenced by authors.

Abundance, 80-83
relative, 466-471
Accipiter cooperii, 109

gentilis, 210-221, 222-228, 229-236, 237-246, 247-252,
264-273, 274-285, 286-295, 296-302, 303-309,
310-323, 32^334, 335-341, 342-350, 439-444
atricapillus, 192-209
laingi, 253-263
Activity centers, 253-263
Adaptive kernel, 253-263
Aegolius acadicus brooksi, 134-141

Agostini, Nicolantonio, Are earlier estimates of Accipitri-
formes crossing the channel of Sicily (Central Med-
iterranean) during spring migration accurate?, 184—
186

Agricultural areas, 55-60
Agriculture, 429-438
Alarm call, 475-476

Alencar Carvalho, Carlos Eduardo, see Mendes de Car-
valho Filho, Eduardo Pio
Allen, Deborah J., see DeCandido, Robert
Anchor-bolt ladder, 109

Andersen, David E., Stephen DeStefano, Michael I. Gold-
stein, Kimberly Titus, Cole Crocker-Bedford, John J.
Keane, Robert G. Anthony, Robert N. Rosenfield,
Technical review of the status of Northern Goshawks
in the western United States, 192-209
Andersen, David E., see Boal, Clint W.

Andersen, David E,, see Smithers, Brett L.

Andrade, Analia, see Sauthier, Daniel E. Udrizar
Anthony, Robert G., see Andersen, David E.
Anthropogenic disturbance, 97-101
Antolin, Michael R, see Bayard de Volo, Shelley
Aquila clanga, 462-466
Argentina, 65-69

Argiielles, Cerafina, see Castellanos, Aradit
Arizona, 274-285
Arkansas, 74-79
Asio otus, 445-453
Athene cuniculania, 429—438
noctua, 156-159, 454—457
Attalea maripa

Baja California, 472-475

Baldassarre, Guy A., see Jensen, Wendy J.

Bayard de Volo, Shelley, Richard T. Reynolds, J. Rick To-
pinka, Bernie May, and Michael F. Antolin, Popula-
tion genetics and genotyping for mark-recapture
studies of Northern Goshawks {Accipiter gentilis) on
the Kaibab Plateau, Arizona, 286—295
Bechard, Marc J., see Fairhurst, Graham D.

Bednarz, J.G., sec Radley, Paul M.

Bednarz, J.G., A Review of Hawks and Owls of Eastern
North America, by Donald S. Heintzelman, 2004,
478-479

Beier, Paul, see Boyce, Douglas A., Jr.

Begall, Sabine, The relationship of foraging habitat to
the diet of Barn Owls ( Tyto alba) from central Ghile,
97-101

Belthoff, James R., see Moulton, Colleen E.

Bennett, Jason R. and P.H. Bloom, Home range and hab-
itat use by Great Horned Owls {Bubo virginianus) m
southern California, 119-126
Bildstein, Keith L., see Jensen, Wendy J.

Bird, David M., see Laing, Dawn K.

Bird, David M., see Chubbs, Tony E.

Black-Hawk, Common, 351-364
Cuban, 351-364

Bloom, Peter H., see Bennett, Jason R.

Bloszyk, Jerzy, see Gwiazdowicz, Dariusz J.

Boal, Clint W., Preface: Proceedings of the international
symposium on the ecology and management of
Northern Goshawks, 189

Boal, Clint W., Productivity and mortality of Northern
Goshawks in Minnesota, 222-228
Boal, Clint W., see Smithers, Brett L.

Boavista, 80-83
Bonin Islands, 173-179
Bootstrapping, 253-263, 274-285
Botella, Francisco, see Navarro, Joan
Boyce, Douglas A., Jr., Patricia L. Kennedy, Paul Beier,
Michael F. Ingraldi, Susie R. MaeVean, Melissa S. Sid-
ers, John R. Squires, and Brian Woodbridge, When
are goshawks not there? Is a single visit enough to
infer absence at occupied nest areas?, 296-302
Brady, Ryan S., see Moulton, Colleen E.

Brazil, southeastern, 89-92
Breeding, 222-228, 229-236
chronology, 74-79
cooperative, 92-94
range, 70-74

484

December 2005

Index to Volume 39

485

British Columbia, 1-10, 335-341
Bubo magellanicus, 163-166
virginianus, 111-118, 119-126
Bustamante, Javier, see Rodriguez, Carlos
Buteo buteo, 466-474
jamaicensis, 108, 439-444
platypterus brunnescens, 404—416
toyoshimai, 173-179
Buteogallus anthracinus, 351-364
gundlachii, 351—364
subtilis, 351-364

Buzzard, Common, 173-179, 466-474

California, southern, 119-126
Calvo, Jose F., see Martinez, Jose E.

Camera, remote, 303-309
Camiha, Alvaro, see Garrido, Jose Rafael
Canary Islands, 186-187
Caprimulgus macrurus, 106-107
Capture-recapture, 286-295
Caracara, Yellow-headed, 94—97
Caribbean, 94—97

Carrete, Martina, see Navarro, Joan

Casado, Eva and Miguel Ferrer, Analysis of reservoir se-
lection by wintering Ospreys {Pandion haliaetus hal-
iaetus) in Andalusia, Spain: a potential tool for re-
introduction, 168-173

Castellanos, Aradit, Cerafina Arguelles, Federico Salinas-
Zavala, Alfredo Ortega-Rubio, New nesting record
and observations of breeding Peregrine Falcons in
Baja California Sur, Mexico, 472-475
Cebus olivaceus, 458—461
Cervera, Francisco, see Garcia, Ana Maria
Chambers, Carol L., see Gatto, Angela E.

Chile, 55-60, 97-101
Chiroptera, 445-453

Chubbs, Tony E., Matthew J. Solensky, Dawn K. Laing,
David M. Bird, and Geoff Goodyear, Using a porta-
ble anchor-bolt ladder to access rock-nesting Osprey,
103-106

see Laing, Dawn K.

Circus spilonotus, 106-107
CITES, 386-393
Colorado, 166—168
Community, 156-159
Competition, 156-159, 439-444
Connecticut, 342-350

Corales Stappung, Ema Soraya, see Rojas, Ricardo A. Fi-
gueroa

Crete, 179-183

Crocker-Bedford, Cole, see Andersen, David E.

Crozier, Michelle L., The effect of broadcasting Great
Horned Owl vocalizations on Spotted Owl vocal re-
sponsiveness, 111-118

DeCandido, Robert and Deborah J. Allen, First nesting
of Cooper’s Hawks {Accipiter cooperii) in New York
City since 1955, 109

Dekker, Dick and Robert Taylor, A change in foraging
success and cooperative hunting by a breeding pair
of Peregrine Falcons and their fledglings, 394-403
de la Rocha, J.L. Paz, see Garrido, Jose Rafael
DeLong, John R, Timothy D. Meehan, and Ruth B.
Smith, Investigating fall movements of hatch-year
Flammulated Owls {Otus flammeolus) in central New
Mexico using stable hydrogen isotopes, 19-25
Departure, 462-466

Desimone, Steven M. and Stephen DeStefano, Temporal
patterns of Northern Goshawk nest area occupancy
and habitat: a retrospective analysis, 310-323
DeStefano, Stephen, see Andersen, David E.

DeStefano, Stephen, see Rogers, Andi S.

DeStefano, Stephen, see Desimone, Steven M.

DeStefano, Stephen, A review of the status and distribu-
tion of Northern Goshawks in New England, 342-
350

Detectability, 274-285
Detection rates, 296-302

Diet, 55-60, 65-69, 80-83, 97-101, 163-166, 173-179,
179-183, 237-246, 264-273, 303-309, 439-444, 445-
453

Digital image analysis, 127-133
Dispersal, 11-18
natal, 253-263
Distance sampling, 237-246
Distribution, 342-350
Doyle, Donald D., see McClaren, Erica L.

Doyle, Frank I., see Mahon, Todd

Eastham, Chris P. and Mike K. Nicholls. Morphometric
analysis of large Falco species and their hybrids with
implications for conservation, 386-393
Eagle, Bald, 1-10, 11-18
Booted, 92-94, 159-163
Greater Spotted, 462-466
Ecology, 351-364

Egea, Maria, see Garrido, Jose Rafael
Eggs, 89-92

Egyptian Vulture, 186-187
Elanoides forficatus, 94—97
Elanus leucurus, 378—385
Elliott, John E., see Elliott, Kyle Hamish
Elliott, Kyle Hamish, Christopher E. Gill, and John E
Elliott, The influence of tide and weather on provi-
sioning rates of chick-rearing Bald Eagles in Vancou-
ver Island, British Columbia, 1-10
Endangered, 404—416

Enderson, James H., Changes in site occupancy and nest-

486

Index to Volume 39

VoL. 39, No. 4

ing performance of Peregrine Falcons in Colorado,
1963-2004, 166-168
Europe, eastern, 36-54
Experiment, cross-over, 111-118

Eairhurst, Graham D. and Marc J. Bechard, Relationships
between winter and spring weather and Northern
Goshawk (Accipiter gentilis) reproduction in northern
Nevada, 229-236
Falco cherrug, 386—393
femoralis, 55-60
naumanni, 12V-133
nexvtoni, 149-155
novaezeelandiae, 386-393

peregrinus, 166-168, 386—393, 394^403, 472—475
rusticolus, 386-393
sparverius, 84—88, 94—97, 378—385
tinnunculus alexandri, 80—83
Falcon, Aplomado 55-60
New Zealand, 386-393

Peregrine, 166-168, 386-393, 394-403, 472-475
Saker, 386-393
Falcons, 378-385
Family break up, 462-466
Feather, 84-88
Feeding ecology, 97-101
Ferland, Cheron, see Forsman, Eric D.

Ferrer, Miguel, see Casado, Eva
Fidelity, site, 134—141
Fish production, 168-173
Fitness, 210-221

Fitzsimons, James A., Attempted predation on a Large-
tailed Nightjar (Caprimulgus macrurus) by an Eastern
Marsh-Harrier ( Circus spilonotus) in coastal Vietnam,
106-107

Fledging-dependency period, 253-263
success, 26-35

Food habits, 429-438, 439-444
niche, 429-438
breadth, 439-444
partitioning, 159-163
Foraging, 439-444
association, 458-461
Forest, 159-163
karst, 404—416

management, 296-302, 324—334
Forsman, Eric D., TimmothyJ. Kaminski, Jeffery C. Lewis,
Kevin J. Maurice, Stan G. Sovern, Cheron Ferland,
and Elizabeth M, Glenn, Home range and habitat
use of Northern Spotted Owls on the Olympic Pen-
insula, Washington, 365-377
Fortabat, Sofia Heinonen, see Pardihas, Ulyses FJ.
French, John B., Jr., see Quinn, Michael J.,Jn
Frye, Graham G., A previously undescribed vocalization
of the Northern Pygmy-Owl, 476-477

Gaibani, Giorgia, see Pandolfi, Massimo
Gangoso, Laura and Cesanjavier Palacios, Ground nest-
ing by Egyptian Vultures {Neophron perenopterus) in
the Canary Islands, 186-187

Garcia, Ana Maria, Francisco Cervera, and Alejandro
Rodriguez, Bat predation by Long-eared Owls m
Mediterranean and temperate regions of southern
Europe, 445-453
Garcia, David, see Navarro, Joan

Garrido, Jose Rafael, Alvaro Camina, Mariangela Guinda,
Maria Egea, Nourdine Mouati, Alfonso Godino, and
J.L. Paz de la Rocha, Absence of the Eurasian Grif-
fon {Gyps fulvus) in northern Morocco, 70-74
Garrido, Orlando H., see Wiley, James W.

Gatto, Angela E., Teryl G. Grubb, and Carol L. Cham-
bers, Red-tailed Hawk dietary overlap with Northern
Goshawks on the Kaibab Plateau, Arizona, 439-444
Gender determination, 127-133
Genetic structure, 192-209
variability, 142-148
Geographical-catchment area, 19-25
Gill, Christopher E., see Elliott, Kyle Hamish
Gimenez, Andres, see Navarro, Joan
Glaucidium gnoma, 476-477
Glenn, Elizabeth M., see Forsman, Eric D.

Godino, Alfonso, see Garrido, Jose Rafael
Goldstein, Michael L, see Andersen, David E.

Gonzalez, Carlos, see Martinez, Jose E.

Gonzalez-Bravo, Betzabeth, see Meraz, Juan
Goodyear, Geoff, see Chubbs, Tony E.

Goshawk, Northern, 192-209, 210-221, 222-228, 229-
236, 237-246, 247-252, 253-263, 264-273, 274-285,
286-295, 296-302, 303-309, 310-323, 324-334, 335-
341, 342-350, 439-444
Gregory, Mark S., see Jensen, Wendy J.

Griffon, Eurasian, 70-74, 179-183

Ground nesting, 186-187

Grubb, Teryl G., see Gatto, Angela E.

Guinda, Mariangela, see Garrido, Jose Rafael
Gutierrez, R.J., see Crozier, Michelle L.

Gwiazdowicz, Dariusz J., Jerzy Bloszyk, Tadeusz Mizera,
and Piotr Tryjanowski, Mesostigmatic mites (Acari
Mesostigmata) in White-tailed Sea Eagle nests {Hal-
iaeetus albicilla) , 60—65
(dyps fulvus, 70-74, 179-183
Gyrfalcon, 386—393

Habitat, 310-323
modek 404—416
relations, 192-"209
use, 119-126, 365-377
Habits, food, 149^155
Haliaeetus dlMcilla, 60—65
leucOcephalus, 1—10, 11-18

December 2005

Index to Volume 39

487

Harrier, Eastern Marsh, 106-107
Hatching success, 26-35
Hawk, Broad-winged, 404-416
Cooper’s, 109
Red-tailed, 108, 439-444
Hawks, 378-385

Hegyi, Zoltan, see Sasvari, Lajos

Hengstenberg, Derek W. and Francisco Vilella, Nesting
ecology and behavior of Broad-winged Hawks in
moist karst forests of Puerto Rico, 404-416
Heterogeneity, individual, 210-221
Hieraaetus pennatus, 92-94, 159-163
Hoffmann, Gyula, see Matics, Robert
Holschuh, Carmen I. and Ken A. Otter, Using vocal in-
dividuality to monitor Queen Charlotte Saw-whet
Owls (Aegolius acadicus brooksi), 134—141
Home range, 119-126, 365-377
Horvath, Gyozo, see Matics, Robert
Honey-buzzard, European, 184—186
Hunting, adult, 394-403
cooperative, 394—403
fledgling, 394-403
tandem, 394—403
Hybrids, falcon, 386-393

IberVNeembucu wetlands, 65-69
Ictinia mississippiensis, 108
Idaho, 429-438

Immature movements, 253—263
Individual identification, 286—295

Ingraldi, Michael F., A skewed sex ratio in Northern Gos-
hawks: is it a sign of a stressed population?, 247-252
Ingraldi, Michael F., see Boyce, Douglas A., Jr.

Ingraldi, Michael F., see Rogers, Andi S.

Introduced animals, 173—179
Introgression, 142-148
Iverson, W.F., 102-103

Juvenile, 11-18

Jensen, Wendy J., Mark S. Gregory, Guy A. Baldassarre,
Francisco Vilella, and Keith L. Bildstein, Raptor
abundance and distribution on the Llanos wedands
of Venezuela, 417-428
Joy, Suzanne M., see Reynolds, Richard T.

Kaibab Plateau, 210-221

Kaminski, TimmothyJ., see Forsman, Eric D.

Kato, Yuka and Tadashi Suzuki, Introduced animals in
the diets of the Ogasawara Buzzard, an endemic in-
sular raptor in the Pacific Ocean, 173-179
Keane, John J., see Andersen, David E.

Kennedy, Patricia L., see Boal, Clint W.

Kennedy, Patricia L., see McClaren, Erica L.

Kennedy, Patricia L., see Boyce, Douglas A., Jr.

Kestrel, Alexander’s, 80-83
American, 84-88, 94-97, 378-385
Common, 80-83
Lesser, 127-133
Madagascar, 149-155
Kite, Black, 184-186
Gray-headed, 89-92
Mississippi, 108
Swallow-tailed, 94-97
White-tailed, 378-385
Klein, Akos, see Matics, Robert
Kowalski, Jan, see Meyburg, Bernd-U.

Labrador, 11-18

Laing, Dawn K., David M. Bird, and Tony E. Chubbs, First
complete migration cycles for juvenile Bald Eagles
{Haliaeetus leucocephalus) from Labrador, 11-18
Laing, Dawn K., see Chubbs, Tony E.

Landscape change, 310-323

Leptodon cayanensis, 89-92

Lewis, Jeffery C., see Forsman, Eric D.

Livezey, Kent B., Iverson (2004) on Spotted Owls and
Barred Owls: comments on methods and conclu-
sion, 102-103
Llanos, 417-428

Maciorowski, Grzegorz, see Meyburg, Bernd-U.

MacVean, Susie R., see Boyce, Douglas A., Jr.

Mahon, Todd and Frank I. Doyle, Effects of timber har-
vesting near nest sites on the reproductive success of
Northern Goshawks {Accipiter gentilis) , 335-341
Maine, 342-350

Management, adaptive, 335-341
Martinez, Jose Antonio, see Zuberogoitia, Inigo
Martinez, Jose E., Carlos Gonzalez, and Jose F. Calvo, Co-
operative nesting by a trio of Booted Eagles {Hieraae-
tus pennatus) , 92-94

Martinez, Jose Enrique, see Zuberogoitia, Inigo
Martinez, Jose E. and Jose F. Calvo, Prey partitioning be-
tween mates in breeding Booted Eagles {Hieraaetus
pennatus), 159-163

Martinez-Cruz, Begona, see Rodriguez, Carlos
Massachusetts, 342-350

Matics, Robert, Sandor Varga, Balazs Opper, Akos Klein,
Gydzo Horvath, Alexandre Roulin, Peter Putnoky,
and Gyula Hoffmann, Partitioning of genetic
(RAPD) variability among sexes and populations of
the Barn Owl {Tyto alba) in Europe, 142-148
Maurice, Kevin J., see Forsman, Eric D.

Mauritia Jlexuosa, 458-461
May, Bernie, see Bayard de Volo, Shelley
McClaren, Erica L., Patricia L. Kennedy, and Donald D
Doyle, Northern Goshawk {Accipiter gentilis laingi)

488

Index to Volume 39

VoL. 39, No. 4

post-fledging areas on Vancouver Island, British Co-
lumbia, 253—263

McNabb, F.M. Anne, see Quinn, Michael J., Jr.
Mediterranean basin, 445-453
central, 184—186

Meehan, Timothy D., see DeLong, John P.

Mendes de Carvalho, Gustavo Diniz, see Mendes de Car-
valho Filho, Eduardo Pio

Mendes de Carvalho Filho, Eduardo Pio, Gustavo Diniz
Mendes de Carvalho, and Carlos Eduardo Alencar
Carvalho, Observations of nesting Gray-headed Kites
{Leptodon cayanensis) in southeastern Brazil, 89-92
Meraz, Juan and Betzabeth Gonzalez-Bravo, First summer
records of Ospreys {Pandion haliaetus) along the
coast of Oaxaca, Mexico, 18V-188
Mesostigmata, 60-65
Mexico, 187-188, 472-475

Meyburg, Bernd-U., Christiane Meyburg, Tadeusz Mizera,
Grzegorz Maciorowski, and Jan Kowalski, Family
break up, departure, and autumn migration in Eu-
rope of a family of Greater Spotted Eagles {Aquila
clanga) as reported by satellite telemetry, 462-466
Meyburg, Christiane, see Meyburg, Bernd-U.

Migration, 11-18, 94—97, 462—466
counts, 184—186
patterns, 19—25
spring, 184-186

Miller, Ikarl E., Red-tailed Hawk depredates Mississippi
Kite nestling at dawn, 108
Milvago chimachima, 94—97
Milvus migrans, 184-186
Minguez, Eduardo, see Navarro, Joan
Minnesota, 222-228, 264-273
Mites, 60-65

Mizera, Tadeusz, see Gwiazdowicz, Dariusz J.

Mizera, Tadeusz, see Meyburg, Bernd-U.

Molecular sexing, 286-295
Molt, 84-88
preformative, 378-385
Monitoring, 274-285
raptor, 324-334

Monkeys, wedge-capped capuchin, 458-461
Morocco, 70-74
Morphometric, 386-393
Mortality, 222-228

Mouati, Nourdine, see Garrido, Jose Rafael
Moulton, Colleen E., Ryan S. Brady, and James R. Belt-
hoff, A comparison of breeding season food habits
of Burrowing Owls nesting in agricultural and non-
agricultural habitat in Idaho, 429-438

Navarro, Joan, Eduardo Minguez, David Garcia, Carlos
Villacorta, Francisco Botella, Jose Antonio Sanchez-
Zapata, Martina Carrete, and Andres Gimenez, Dif-
ferential effectiveness of playbacks for Little Owls

{Athene noctua) surveys before and after sunset, 454—
457

Negro, Juan Jose, see Rodriguez, Carlos
Neophron percnopterus, 1 86-1 87
Neotropics, 417-428
Nest alternate, 274-285
area, 296-302, 335-341
historical, 310-323
biology 60-65, 89-92
depredation, 108
structure, 89-92
success, 404-416
Nesting, 109

biology, 89-92, 149-155
record, 472-475

Nesting structures, artificial, 74-79

Nestling, 89-92, 127-133, 247-252

Nests, 149-155

Nevada, 229-236

New England, 342-350

New Hampshire, 342-350

New York City, 109

Nicholls, Mike K., see Eastham, Chris P.

Nightjar, Large-tailed, 106-107

Nijman, Vincent, Tineke G. Prins, andJ.H. (Hans) Reu-
ter, Timing and abundance of migrant raptors on
Bonaire, Netherlands Antilles, 94-97
Noon, Barry R., see Salafsky, Susan R.

Oaxaca, 187-188
Occupancy, 296-302
nest site, 324-334
rate, 166-168

Ogasawara Islands, 173-179
Olympic Peninsula, 365-377

Ontiveros, Diego, Abundance and diet of Alexander’s
Kestrel {Falco tinnunculus alexandri) on Boavista Is-
land (Archipelago of Cape Verde), 80-83
Opper, Balazs, see Matics, Robert
Oregon, 310-323

Ortega-Rubio, Alfredo, see Castellanos, Aradit
Osprey, 103-106, 168-173, 187-188
Otter, Ken A., see Holschuh, Carmen I.

Ottinger, Mary Ann, see Quinn, Michael J., Jr.

Otus Jlammeolus, 19—25
scops, 156-159

Owl, Barn, 65-69, 74-79, 97-101, 142-148, 156-159,
163-166

Barred, 102-103
Burrowing, 429-438
California Spotted, 111-118
Flammulated, 19-25
Great Horned, 111-118, 119-126
Little, 156-159, 454-457
Long-eared, 445-453

December 2005

Index to Volume 39

489

Magellanic Horned, 163-166
Northern Saw-whet, 134-141
Northern Spotted, 184—186, 365-377
Rufous-legged, 163-166
Scops, 156-159
Tawny, 26-35, 156-159

Palacios, Cesar-Javier, see Gangoso, Laura
Palms, Attalea maripa, 458-461
Pandion haliaetus, 103-106, 168-173, 187-188
Pandolfi, Massimo, Alessandro Tanferna, and Giorgia
Gaibani, Seasonal patterns of Common Buzzard (Bu-
teo buteo) relative abundance and behavior in Pollino
National Park, Italy, 466-471
Paraguay, 65—69

Pardihas, Ulyses F.J., see Sauthier, Daniel E. Udrizar
Pardihas, Ulyses F.J., Pablo Teta, and Sofia Heinonen For-
tabat. Vertebrate prey of the Barn Owl ( Tyto alba) in
subtropical wetlands of northeastern Argentina and
eastern Paraguay, 65-69
Parental age, 26-35
condition, 26-35

Patla, Susan M., Monitoring results of Northern Goshawk
nesting areas in the greater Yellowstone ecosystem:
is decline in occupancy related to habitat change?,
324-334
PGA, 386-393
Pellet analysis, 179-183
Pernis apivorus, 184—186
Playback effectiveness, 454-457
Plumage, 84-88
Poland, 60-65
Polygamy, 92-94
Polygyny, 92-94
Population change, 166-168
status, 36-54
trend, 192-209, 229-236
Predation, 156-159
attempted, 106—107
Predator-prey dynamics, 237-246
Predictive model, 168-173
Prey biomass, 65-69
delivery, 404—416
rate, 303-309
density, 237-246
diversity, 264-273
provisioning, 159-163
Principal component analysis, 386-393
Pnns, Tineke G., see Nijman, Vincent
Probability of identity, 286-295

Productivity, 1-10, 74-79, 149-155, 166-168, 222-228,
237-246

Puerto Rico, 404—416

Putnoky, Peter, see Matics, Robert

Pygmy-Owl, Northern, 476-477

Pyle, Peter, First-cycle molts in North American Falconi-
formes, 378-385

Quinn, Micheal Jr., John B. French, Jr., F.M. Anne
McNabb, and Mary Ann Ottinger, The role of thy-
roxine on the production of plumage in the Amer-
ican Kestrel {Falco sparverius) , 84—88

Rabearivony, Jeanneney, see Rene de Roland, Lily-Arison
Radiotelemetry, 365-377

Radley, Paul M. and James C. Bednarz, Artificial nest
structure use and reproductive success of Barn Owls
in northeastern Arkansas, 74-79
RAPD, 142-148

Razafimanjato, Gilbert, see Rene de Roland, Lily-Arison
Recruitment, 210-221
Reintroduction, 168-173

Rene de Roland, Lily-Arison, Jeanneney Rabearivony,
Harilalaina Robenarimangason, Gilbert Razafiman-
jato, and Russell Thorstrom, Breeding biology and
food habits of the Madagascar Kestrel {Falco newtom)
in northeastern Madagascar, 149-155
Reproduction, 274-285

Reproductive success, 74-79, 102-103, 166-168, 210-221,
335-341

Reservoirs, 168-173
Response, heterospecific, 111-118
Reuter, J.H. (Hans), see Nijman, Vincent
Reversed size dimorphism (RSD), 159-163
Review, 192-209

Reynolds, Richard T., In raemoriam: Suzanne Merideth
Joy, 190-191

Reynolds, Richard T., see Wiens, J. David
Reynolds, Richard T., see Salafsky, Susan R.

Reynolds, Richard T, J. David Wiens, Suzanne M. Joy,
and Susan R. Salafsky, Sampling considerations for
demographic and habitat studies of Northern Gos-
hawks, 274—285

Reynolds, Richard T, see Bayard de Volo, Shelley
RGB values, 127-133
Rhode Island, 342-350

Robenarimangason, Harilalaina, see Rene de Roland,
Lily-Arison

Rodents, sigmodontine, 163-166
Rodriguez, Alejandro, see Garcia, Ana Maria
Rodriguez, Carlos, Javier Bustamante, Begona Martinez-
Cruz, and Juan Jose Negro, Evaluation of methods
for gender determination of Lesser Kestrel nestlings,
127-133

Rogers, Andi S., Stephen DeStefano, and Michael F. In-
graldi. Quantifying Northern Goshawk diets using
remote cameras and observations from blinds, 303-
309

Rojas, Ricardo A. Figueroa and Ema Soraya Corales Stap-
pung, Seasonal diet of the Aplomado Falcon {Falco

490

Index to Volume 39

VoL. 39, No. 4

femaralis) in an agricultural area of Araucania, south-
ern Chile, 55—60

Rosenfield, Robert N., see Andersen, David E.

Roulin, Alexandre, see Matics, Robert

Salafsky, Susan R., Richard T. Reynolds, and Barry R.
Noon, Patterns of temporal variation on goshawk re-
production and prey resources, 237-246
Salafsky, Susan R., see Reynolds, Richard T.
Sahnas-Zavala, Federico, see Castellanos, Aradit
Sampling, 274-285
repeated, 296-302

Sanchez-Zapata, Jose Antonio, see Navarro, Joan
Sarcoramphus papa, 458-461

Sasvari, Lajos and Zoltan Hegyi, Effects of breeding ex-
perience on nest-site choice and the reproductive
performance of Tawny Owls {Strix aluco), 26-35
Satellite telemetry, 11-18, 462-466

Sauthier, Daniel E. Udrizar, Analia Andrade, and Ulyses
FJ. Pardihas, Predation of small mammals by Rufous-
legged Owl, Barn Owl, and Magellanic Horned Owl
in Argentinian Patagonia Forests, 163-166
Savanna, 417-428

Schlee, Marsha A., King Vultures {Sarcoramphus papa) for-
age in moriche and cucurit palm stands, 458-461
Sea Eagle, White-tailed, 60-65
Seamons, Mark E., see Crozier, Michelle L.

Sex allocation, 247-252
ratio, 247-252
Sicily, Channel of, 184—186
Siders, Melissa S., see Boyce, Douglas A., Jr.

Smith, Ruth B., see DeLong, John P.

Smithers, Brett L., Clint W. Boal, and David E. Andersen,
Northern Goshawk diet in Minnesota: an analysis us-
ing video recording systems, 264—273
Solensky, Matthew J., see Chubbs, Tony E.

Severn, Stan G., see Forsman, Eric D.

Spain, southern, 168-173

Squires, John R., see Boyce, Douglas A., Jr.

Squirrel, red, 264-273
Stable-hydrogen isotopes, 19-25
Status, 192-209, 342-350
Stopover, 11-18
Stnx aluco, 26-35, 156-159
occidentalis caurina, 365-377
occidentalis, 102-103, 111-118
rufipes, 163-166
varia, 102—103
Subspecies, 142-148
Insular 173—179
Success, reproductive, 166—168
Survey, auditory, 111-118
method, 454—457
population, 454—457
roadside, 417-428, 466-471

techniques, 324—334
Suzuki, Tadashi, see Kato, Yuka

Tagging, genetic, 286-295

Tamiasciurus hudsonicus, 264—273

Tanferna, Alessandro, see Pandolfi, Massimo

Taxonomy, 351-364

Taylor, Robert, see Dekker, Dick

Techniques, 103-106

Territoriality, 111-118

Territory occupancy, 274—285

Teta, Pablo, see Pardihas, Ulyses FJ.

Thorstrom, Russell, see Rene de Roland, Lily-Arison
Threats, 36-54
Thyroxine, 84—88
Tides, 1-10

Timber harvesting, 335-341

Titus, Kimberly, see Andersen, David E.

Topinka, J. Rick, see Bayard de Volo, Shelley
Trio, 92-94

Trophic plasticity, 445-453

Tryjanowski, Piotr, see Gwiazdowicz, Dariusz J.

Turan, Levent, The status of diurnal birds of prey in Tur-
key, 36—54
Turkey, 36-54

Tyto alba, 65-69, 97-101, 142-148, 156-159, 163-166
pratincola, 74-79

United States, northeastern, 342-350
western, 192-209

Varga, Sandor, see Matics, Robert
Venezuela, 417-428
Vermont, 342-350
Video surveillance, 303—309
Vietnam, 106—107

Vilella, Francisco, see Jensen, Wendy J.

Vilella, Francisco, see Hengstenberg, Derek W.
Villacorta, Carlos, see Navarro, Joan
Vocal individuality, 134—141
Vocalization, 476—477
Vulture, King, 458-461

Washington, 365-377
Weather, 1-10, 229-236
condition, 26-35
Wetlands, 417-428

Wiens, J. David and Richard T. Reynolds, Is fledging suc-
cess a reliable index of fitness in Northern Gos-
hawks?, 210-221

Wiens, J. David, see Reynolds, Richard T.

Wiley, James W. and Orlando H. Garrido, Taxonomic sta-

December 2005

Index to Volume 39

491

tus and biology of the Cuban Black-Hawk, Buteogallus
anthracinus gundlachii (Aves: Accipitridae) , 351—364
Wintering, 70-74

Woodbridge, Brian, see Boyce, Douglas A., Jr.

Xirouchakis, Stavros M., The diet of Eurasian Griffons
{Gyps fulvus) in Crete, 179-183

Zabala, Jabi, see Zuberogoitia, Inigo

Zuberogoitia, Inigo, Jose Antonio Martinez, Jabi Zabala,
and Jose Enrique Martinez, Interspecific aggression
and nest-site competition in a European owl com-
munity, 156-159

THE JOURNAL OF RAPTOR RESEARCH

A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.

(Founded 1966)

EDITOR IN CHIEF
James C. Bednarz

ASSOCIATE EDITORS

James R. Belthoff
Clint W. Boal
Cheryl R. Dykstra
Michael I. Goldstein

Joan L. Morrison
Fabrizio Sergio
Ian G. Warrentin
James W. Watson

BOOK REVIEW EDITOR

Jeffrey S. Marks

CONTENTS FOR VOLUME 39, 2005

Number 1

The Influence of Tide and Weather on Provisioning Rates of Chick-rearing
Bald Eagles in Vancouver Island, British Columbia. Kyle Hamish Elliott,

Christopher E. Gill, and John E. Elliott 1

First Complete Migration Cycles for Juvenile Bald Eagles {Haliaeetus

LeUCOCEPHALUS) from Labrador. Dawn K. Laing, David M. Bird, and Tony E. Chubbs ........ 11

Investigating Fall Movements of Hatch-year Flammulated Owls ( Otus

FLAMMEOLUS) IN CENTRAL NeW MEXICO USING STABLE HYDROGEN ISOTOPES.

John P. DeLong, Timothy D. Meehan, and Ruth B. Smith 19

Effects of Breeding Experience on Nest-site Choice and the Reproductive
Performance of Tawny Owls (Strix aluco) . Lajos Sasvari and Zoitan Hegyi 26

The Status of Diurnal Birds of Prey in Turkey. Levent Turan 36

Short Communications

Seasonal Diet of the Aplomado Falcon (Falco femoralis) in an Agricultural Area of Araucania,

Southern Chile. Ricardo A. Figueroa Rojas and Ema Soraya Corales Stappung 55

Mesostigmatic Mites (Acari: Mesostigmata) in White-tailed Sea Eagle Nests {Haliaeetus albicilla) .

Dariusz J. Gwiazdowicz, Jerzy Bloszyk, Tadeusz Mizera, and Piotr Tryjanowski 60

Vertebrate Prey of the Barn Owl ( Tyto alba) in Subtropical Wetlands of Northeastern

Argentina and Eastern Paraguay. Ulyses FJ. Pardinas, Pablo Teta, and Sofia Heinonen Fortabat 65

Absence of the Eurasian Griffon {Gyps fulvus) in Northern Morocco. Jose Rafael Garrido,

Alvaro Camiha, Mariangela Guinda, Marfa Egea, Nourdine Mouati, Alfonso Godino, and

J.L. Paz de la Rocha 70

Artificial Nest Structure Use and Reproductive Success of Barn Owls in Northeastern

Arkansas. Paul M. Radley and James C. Bednarz 74

Abundance and Diet of Alexander’s Kestrel {Falco tinnunculus alexandri) on Boavista Island

(Archipelago of Cape Verde) . Diego Ontiveros 80

The Role of Thyroxine on the Production of Plumage in the American

Kestrel {Falco sparverius) . Michael J. Quinn, Jr., John B. French, Jr., F.M. Anne McNabb,

and Mary Ann Ottinger 84

Observations of Nesting Gray-headed Kites {Leptodon cayanensis) in Southeastern Brazil.

Eduardo Pio Mendes de Carvalho Filho, Gustavo Diniz Mendes de Carvalho, and Carlos Eduardo
Aencar Carvalho 89

Cooperative Nesting by a Trio of Booted Eagles {Hieraaetus pennatus). Jose E. Martmez,

Carlos Gonzalez, and Jose F. Calvo 92

Timing and Abundance of Migrant Raptors on Bonaire, Netherlands Antilles. Vincent Nijman,

Tineke G. Prins, andJ.H. (Hans) Reuter 94

The Relationship of Foraging Habitat to the Diet of Barn Owls ( Tyto alba) from Central Chile.

Sabine Begall 97

Letters

Iverson (2004) on Spotted Owls and Barred Owls: Comments on Methods and Conclusion.

Kent B. Livezey 102

Using a Portable, Anchor-bolt Ladder to Access Rock-nesting Osprey. Tony E. Ghubbs,

Matthew J. Solensky, Dawn K. Laing, David M. Bird, and Geoff Goodyear 103

Attempted Predation on a Large-tailed Nightjar ( Caprimulgus macrurus) by an Eastern

Marsh-Harrier (Circus spilonotus) in Coastal Vietnam. James A. Fitzsimons 106

Red-tailed Hawk Depredates Mississippi Kite Nestling at Dawn. Karl E. Miller 108

First Nesting of Cooper’s Hawks (Accipiter cooperu) in New York City Since 1955 .

Robert DeCandido 1 09

Manuscript Referees 110

Number 2

The Effect of Broadcasting Great Horned Owl Vocalizations on Spotted Owl

Vocal Responsiveness. Michelle L. Crozier, Mark E. Seamans, and R.J. Gutierrez Ill

Home Range and Habitat Use by Great Horned Owls {Bubo virginianus) in

Southern California. Jason R. Bennett and Peter H. Bloom 119

Evaluation of Methods for Gender Determination of Lesser Kestrel Nestlings.

Carlos Rodriguez, Javier Bustamante, Begona Martmez-Cruz, and Juan Jose Negro 127

Using Vogal Individuality to Monitor Queen Charlotte Saw-whet Owls

(AeGOLIUS ACADICUS BROOKS !) . Carmen I. Holschuh and Ken A. Otter 134

Partitioning of Genetic (RAPD) Variability among Sexes and Populations
OF THE Barn Owl ( TyTO alba) in Europe. Robert Matics, Sandor Varga, Balazs Opper,

Akos Klein, Gyozo Horvath, Alexandre Roulin, Peter Putnoky, and Gyula Hoffmann 142

Breeding Biology and Food Habits of the Madagascar Kestrel {Falco newtoni)

IN Northeastern Madagascar. Lily-Arison Rene de Roland, Jeanneney Rabearivony,

Harilalaina Robenarimangason, Gilbert Razafimanjato, and Russell Thorstrom 1 49

Short Communications

Interspecific Aggression and Nest-site Competition in a European Owl Community.

Inigo Zuberogoitia, Jose Antonio Martinez, Jabi Zabala, and Jose Enrique Martinez 156

Prey Partitioning between Mates in Breeding Booted Eagles (Hieraaetus pennatus) .

Jose E. Martinez and Jose F. Calvo 159

Predation of Small Mammals by Rufous-legged Owl, Barn Owl, and Magellanic Horned Owl
IN Argentinean Patagonia Forests. Daniel E. Udrizar Sauthier, Analia Andrade, and
Ulyses F. J. Pardinas 163

Changes in Site Occupancy and Nesting Performance of Peregrine Falcons in Colorado,

1963-2004. James H. Enderson 166

Analysis of Reservoir Selection by Wintering Ospreys (Pandion haliaetus hauaetus) in Andalusia, Spain:

A Potential Tool for Reintroduction. Eva Casado and Miguel Ferrer 168

Introduced Animals in the Diets of the Ogasawara Buzzard, an Endemic Insular Raptor in

the Pacific Ocean. Yuka Kato and Tadashi Suzuki 173

The Diet of Eurasian Griffons {Gyps fulvus) in Crete. Stavros M. Xirouchakis

179

Letters

Are Earlier Estimates of Accipitriformes Crossing the Channel of Sicily (Central Mediterranean)

During Spring Migration Accurate? Nicolantonio Agostini 184

Ground Nesting by Egyptian Vultures {Neophron percnoptekus) in the Canary Islands.

Laura Gangoso and Cesar-Javier Palacios 186

First Summer Records of Ospreys {Pandion haliaetus) Along the Coast of Oaxaca, Mexico.

Juan Meraz and Betzabeth Gonzalez-Bravo 187

Number 3

Introduction

Preface: Proceedings of the International Symposium on the Ecology and Management of

Northern Goshawks. Clint W. Boal 189

In Memoriam: Suzanne Merideth Joy. Richard T. Reynolds 190

Status

Technical Review of the Status of Northern Goshawks in the Western United States.

David E. Andersen, Stephen DeStefano, Michael I. Goldstein, Kimberly Titus, Cole
Crocker-Bedford, John J. Keane, Robert G. Anthony, and Robert N. Rosenfield 192

Biology

Is Fledging Success a Reliable Index of Fitness in Northern Goshawks?

J. David Wiens and Richard T Reynolds 210

Productivity and Mortai.ity of Northern Goshawks in Minnesota.

Clint W. Boal, David E. Andersen, and Patricia L. Kennedy 222

Relationships Between Winter and Spring Weather and Norihern Goshawk {AcapiTER gentilis)

Reproduction in Northern Nevada. Graham D. Fairhurst and Marc J. Bechard 229

Patterns of Temporal Variation in Goshawk Reproduction and Prey Resources.

Susan R. Salafsky, Richard T. Reynolds, and Barry R. Noon 237

A Skewf.d Sex Ratio in Northern Goshawks; Is It a Sign of a Stressed Population?

Michael E Ingraldi 247

Northern Goshawk {Accjpiter gentilis laingi) Post-fledging Areas on Vancouver Isiand, British

Columbia. Erica L. McClaren, Patricia L. Kennedy, and Donald D. Doyle 253

Northern Goshawk Diet in Minnesota: An Anaiasis Using Video Recording

Systems. Brett L. Smithers, Clint W. Boal, and David A. Andersen 264

Techniques

Sampling Considerations for Demographic and Habitat Studies of Northern Goshawks.

Richard T. Reynolds, J. David Wiens, Suzanne M. Joy, and Susan R. Salafsky 274

Population Genetics and Genotyping for Mark-Recapture Studies of Northern Goshawks
{Acciitper gentilis) on the Kaibab Plateau, Arizona. Shelley Bayard de Volo, Richard T.

Reynolds, J, Rick Topinka, Bernie May, and Michael F. Antolin 286

When Are Goshawks Not There? Is a Single Visit Enough to Infer Absence at Occupied Nest
Areas? Douglas A. Boyce, Jr., Patricia L. Kennedy, Paul Beier, Michael F. Ingraldi,

Susie R. MacVean, Melissa S. Siders, John R. Squires, and Brian Woodbridge 296

Quantifying Northern Goshawk Diets Using Remote Cameras and Observations

from Blinds. Andi S. Rogers, Stephen DeStefano, and Micheal F. Ingraldi 303

Conservation

Temporal Pati'erns of Northern Goshawk Nest Area Occupancy and Habitat: A Retrospective

Anai.ysis. Steven Desimone and Stephen DeStefano 310

Monitoring Results of Northern Goshawk Nesting Areas in the Greater Yellowstone Ecosystem:

Is Decline in Occupancy Reiated to Habitat Change? Susan M. Patla 324

Effects of Timber Harvesting Near Nest Sites on the Reproductive Success of Northern

Goshawks {Accipiter gentius). Todd Mahon and Frank I. Doyle 335

A Review of the Status and Distribution of Northern Goshawks in New England.

Stephen DeStefano 342

Number 4

Taxonomic Status and Biology of the Cuban Black-Hawk, Buteogallus

ANTHRACINUS GUNDLACHII (AVES: AcCIPITRIDAE) . James W. Wiley and Orlando H. Garrido.... 351

Home Range and Habitat Use of Northern Spotted Owls on the Olympic

Peninsula, Washington. Eric D. Forsman, TimmothyJ. Kaminski, Jeffery C. Lewis,

Kevin J. Maurice, Stan G. Sovern, Cheron Ferland, and Elizabeth M. Glenn 365

First-cycle Molts in North American Falconiformes. Peter Pyle 378

Morphometric Analysis of Large Falco Species and Their Hybrids with
Implications for Conservation. Chris p. Eastham and Mike k. Nichoiis 386

A Change in Foraging Success and Cooperative Hunting by a Breeding Pair

OF Peregrine Falcons and Their Fledglings. Dick Dekker and Robert Taylor 394

Nesting Ecology and Behavior of Broad-winged Hawks in Moist Karst

Forests of Puerto Rico. Derek W. Hengstenberg and Francisco J. Vilella 404

Raptor Abundance and Distribution in the Llanos Wetlands of Venezuela.

Wendy J. Jensen, Mark S. Gregory, Guy A. Baldassarre, Francisco J. Vilella, and Keith L. Bildstein .... 417

A Comparison of Breeding Season Food Habits of Burrowing Owls Nesting
IN Agricultural and Nonagricultural Habitat in Idaho. Colleen e. Moulton,

Ryan S. Brady, and James R. Belthoff 429

Red-tailed Hawk Dietary Overlap with Northern Goshawks on the Kaibab

Plateau, Arizona. Angela E. Gatto, Teryl G. Grubb, and Carol L. Chambers 439

Bat Predation by Long-eared Owls in Mediterranean and Temperate Regions

OF Southern Europe. Ana Marfa Garcfa, Francisco Cervera, and Alejandro Rodriguez 445

Short Communications

Differential Effectiveness of Playbacks for Little Owls {Athene noctua) Surveys before and
AFTER Sunset. Joan Navarro, Eduardo Mfnguez, David Garcfa, Carlos Villacorta, Francisco
Botella, JosJ Antonio S<nchez-Zapata, Martina Carrete, and Andijs Gimjnez 454

King Vultures {Sarcoramphus papa) Forage in Moriche and Cucurit Palm Stands. Marsha A. Schlee 458

Seasonal Patterns of Common Buzzard {Buteo buieo) Relative Abundance and Behavior in

POLLINO National Park, Italy. Massimo Pandolfi, Alessandro Tanferna, and Giorgia Gaibani 466

New Nesting Record and Observations of Breeding Peregrine Falcons in Baja California Sur,

Mexico. Aradit Castellanos, Cerafma Argiielles, Federico Salinas-Zavala, and Alfr edo Ortega-Rubio 472

Letters

A Previously Undescribed Vocalization of the Northern Pygmv-Owl. Graham G. Frye 476

Book Review. Edited by Jeffrey S. Marks 478

Information for Contributors 480

Index to Volume 39 484

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2006 ANNUAL MEETING

The Raptor Research Foundation, Inc. 2006 annual meeting will be held in conjunction with the
Fourth North American Ornithological Conference on 3-7 October 2006 in Veracruz, Mexico. For
more information about the meeting see http:/ /www.naoc2006.org/

Persons interested in predatory birds are invited to join The Raptor Research Foundation, Inc. (see:
http:/ /biology.boisestate.edu/ raptor/). Send requests for information concerning membership, subscriptions,
special publications, or change of address to OSNA, 5400 Bosque Blvd., Suite 680, Waco TX 76710, U.S.A.

The, Journal of Raptor Research (ISSN 0892-1016) is published quarterly and available to individuals for $40.00
per year and to libraries and institutions for $65.00 per year from The Raptor Research Foundation, Inc., 14377
1 17th Street South, Hastings, Minnesota 55033, U.S.A. (Add $3 for destinations outside of the continental United
States.) Periodicals postage paid at Hastings, Minnesota, and additional mailing offices. POSTMASTER: Send
address changes to The Journal of Raptor Research, OSNA, P.O. Box 1897, Lawrence, KS 66044-8897, U.S.A.

Printed by Allen Press, Inc., Lawrence, Kansas, U.S.A.

@ This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).

Raptor Research Foundation, Inc.

Grants and Awards

For details and additional information visit:
http:/ /biology.boisestate.edu/raptor/grants%20and%20awards.htm

Awards for Recognition of Significant Contributions

The Tom Cade Award is a non-monetary award that recognizes an individual who has made significant advances
in the area of captive propagation and reintroduction of raptors. The Fran and Frederick Hamerstrom
Award is a non-monetary award that recognizes an individual who has contributed significantly to the under-
standing of raptor ecology and natural history. Submit nominations for either award to: Dr. Clint Boal, Texas
Cooperative Fish and Wildlife Research Unit, BRD/USGS, Texas Tech University, 15th Street & Boston,
Ag Science Bldg., Room 218, Lubbock TX 79409-2120 U.S.A.; phone: 806-742-2851; e-mail: cboal@ttu.edu

Awards for Student Recognition and Travel Assistance

The James R. Koplin Travel Award is given to a student who is the senior author and presenter of a paper or
poster to be presented at the RRF meeting for which travel funds are requested. Application deadline: due
date for meeting abstract. Contact: Dr. Patricia A. Hall, 5937 E. Abbey Rd., Flagstaff, AZ 86004; phone:
520-526-6222 U.S.A.; e-mail: pah@spruce.for.nau.edu

The William C. Anderson Memorial Award is given to both the best student oral and poster presentation at the
annual RRF meeting. The paper cannot be part of an organized symposium to be considered. Application
deadline; due date for meeting abstract, no special application is needed. Contact: Rick Gerhardt, Sage
Science, 319 SE Woodside Ct., Madras, OR 97741 U.S.A; phone: 541-475-4330; email; rgerhardt@madras.net

Grants

Application deadline for all grants is February 15 of each year; selections will be made by April 15.

The Dean Amadon Grant for up to $1000 is designed to assist persons working in the area of systematics (tax-
onomy) and distribution of raptors. The Stephen R. TuUy Memorial Grant for up to $500 is given to sup-
port research and conservation of raptors, especially to students and amateurs with limited access to alter-
native funding. Agency proposals are not accepted. Contact for both grants; Dr. Carole Griffiths, 251
Mar ding Ave., Tarrytown, NY 10591 U.S.A.; phone: 914-631-2911; e-mail; cgriff@liu.edu

The Leslie Brown Memorial Grant for up to $1400 is given to support research and/or the dissemination of
information on African raptors. Contact: Dr. Jeffrey L. Lincer, 9251 Golondrina Drive, La Mesa, CA 91941,
U.S.A.; e-mail: JeflLincer@tns.net

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